I presume you're referring to self-loading firearms. In fact, the rifles used by the major combatants in WWI were all 'repeaters,' as the term is used in firearms history. A repeating firearm is any firearm that doesn't have to be reloaded after each shot. So, a revolver is a form of a repeater, as is a lever-action Winchester, and so are the Short Magazine Lee-Enfields, the Mauser Gewehr 98s, the Lebel 1886s, the Mosin-Nagants, and the Steyr-Mannlicher M95s the major WWI combatants primarily employed. Each of those weapons have magazines, usually five but sometimes eight or ten rounds in capacity. And so, while the soldier did need to work a bolt to rechamber between each shot, he did not have to reload the gun between each shot. Thus, repeaters.

As to why the combatants didn't employ self-loading small arms (that is, semi-automatic firearms, which rechamber automatically using leftover force from firing, whether gas or recoil, and thus can be fired as fast as the soldier can pull the trigger, or fully automatic firearms, which do all of that but on which you can simply hold down the trigger), it's a matter of technology.

At the time of WWI, smokeless powder repeating small arms were both sort of on the bleeding edge of firearm technology, and also almost obsolete, at the same time. Self-loading technology was well known, and widespread in the form of heavy, water-cooled machine guns. There were also well-known prototypes of self-loading small arms, which had cropped up occasionally in pre-war firearms trials throughout Europe, and everyone wanted them, for obvious reasons.

However, self-loading small arms technology was, at the time, quite rudimentary, and there were serious issues with virtually every part of the technology, from creating weapons strong enough to withstand so much firing and also light enough to use, recoil issues, overheating issues, accidental fully automatic fire issues (contrary to what you might expect, fully automatic weapons are much easier to make than semi-automatic, which require a disconnector or sere to prevent full auto), manufacturing capacity, considerably greater expense than a normal bolt-action (automatic firearms have many more moving parts than non-automatic), and perhaps the biggest issue, aside from cost: cycling.

That is, there were very few self-loading small arms at the time that would reliably run through the entire process of firing and rechambering without intervention from the soldier. That process, in theory, goes like this: (1) first round in magazine manually chambered by soldier; (2) trigger pulled; (3) hammer/striker drops; (4) primer ignites; (5) propellant ignites; (6) bullet leaves jacket then barrel; (7) recoil of firing or gas piston (fed by propellant gas) forces the bolt carriage and assembly back; (8) re-cocking hammer/striker; (9) exposing the spent casing to the ejection port; (10) sere and trigger reset; (11) extractor ejects spent casing; (12) bolt carriage moves forward, picking up another cartridge from magazine, which is chambered when the bolt carriage comes to rest and locks; (13) ready to fire again.

In general, each of these things had to happen in a few milliseconds, and if any one of these went wrong even slightly, the gun wouldn't be automatically ready to fire again, and the soldier would have to fiddle with it.

As a result of these difficulties, and the enormous cost of equipping everyone with a self-loading rifle, the combatants of WWI focused their budget for infantry equipment where it would do the most good: heavy and light machine guns, the latter of which made an especially large impression on the minds of all the combatants.

The French are an especially interesting case study in this regard. The French were the first to perfect smokeless powder, and they wanted to capitalize on their advantage as much as they possibly could, so they rushed development of a rifle to go along with the smokeless powder, which would ultimately be the Lebel 1886, the first smokeless powder repeating rifle. But this approach had major drawbacks, especially because there was no great European war soon after 1886. But, because they rushed, their gun lacked many of the features that would be regarded as fairly essential during the actual war, and which the other combatants' weapons had. First and foremost, the Lebel 1886 did not have a box magazine; it had a tube magazine (like a Winchester or a shotgun), and so each bullet had to be loaded individually. Other, more modern weapons could load 5 cartridges at a time. Also, the 8mm Lebel cartridge had a distinct taper (essentially, the bullet resembled a cone rather than a cylinder), which was fairly standard at the time of the Lebel rifle was designed. But the tapered cartridge could not be put into belts or flexible links, which were critical for machine guns. As a result, French machine guns were fed from long, rigid steel clip magazines, which was ultimately adequate, but were cumbersome and were more labor-intensive for the loader, since they only held about 30 rounds each.

These failings would become acute during the war, and so the French were the first to really look into replacing their bolt-action rifles with self-loading ones, and they did this during the war. The end result was the RSC 1917, of which about 90,000 were made during the war, and these were actually used. Its performance was good for a weapon that was so hastily developed, and the French planned to massively increase deployment of them for the 1919 spring campaign, which ultimately did not happen. The British also had a self-loader that they intended to deploy in 1919, the Farquhar-Hill.

The French did have one very notable hit of a small(ish) arm during WWI: the Chauchat. The weapon has a very poor reputation in the USA, but it is largely not deserved. The low reputation is attributable to the (actually bad) Chauchats chambered in .30-06, which the French made for American forces in Europe. The Chauchat chambered in 8mm Lebel was an extremely effective weapon, and the French had a very large number of them.

After the war, however, all the same limitations came back up, and almost no one replaced their bolt-actions with self-loaders. Even the most famous user of self-loaders in WWII, the USA, did not completely equip its infantry with them until after the US entered the war. The USMC fought a substantial chunk of the Pacific War with bolt-action Springfield rifles.

If you're wondering why the French didn't stick with the RSC after the war, given its adequacy, the answer is that the French wanted to completely overhaul their small arms, and especially to get rid of the 8mm Lebel cartridge. They partially succeeded in this, in the end. They designed a new, non-tapered rifle cartridge, the 7.5mm French, and designed new weapons to go with it. The French invested most of their time and money into the light machine gun, which produced FM 24/29, a very fine weapon that was widely deployed in the French army before WWII. As to rifles, the French wanted to design a self-loader for the new 7.5mm cartridge, but were unable to do so due to budget cuts and the like. Instead, they designed a new bolt-action rifle, the MAS-36, for the new cartridge as a stop-gap, even though they knew bolt-actions were obsolete.

Hey there,

Just to let you know, your question is fine, and we're letting it stand. However, you should be aware that questions framed as 'Why didn't X do Y' relatively often don't get an answer that meets our standards (in our experience as moderators). There are a few reasons for this. Firstly, it often can be difficult to prove the counterfactual: historians know much more about what happened than what might have happened. Secondly, 'why didn't X do Y' questions are sometimes phrased in an ahistorical way. It's worth remembering that people in the past couldn't see into the future, and they generally didn't have all the information we now have about their situations; things that look obvious now didn't necessarily look that way at the time.

If you end up not getting a response after a day or two, consider asking a new question focusing instead on why what happened did happen (rather than why what didn't happen didn't happen) - this kind of question is more likely to get a response in our experience. Hope this helps!