Swords were primarily a sidearm for most of history. Weapons with greater reach such as spears (and eventually more developed polearms) were generally the primary weapon for a medieval infantry soldier. Swords also developed alongside armor, in order to compensate for increased levels of protection in a sort of medieval arms race. As armor became more protective, swords gained more profile taper (became narrower), and often had less distal taper (became stiffer as a result). This was intended to allow for halfswording techniques, where the blade was grabbed halfway up in order to aid in tip control, so you could shove the tip of the blade into gaps in your opponent's armor.

Evidence of this evolutionary arms race can be seen in Eward Oakeshotts Records of the Medieval Sword, which presents a typology of medieval swords, including the variations in blade profile and blade geometry, indicating the development of more specialised thrusting swords with narrow but thick blades intended to combat armor.

But returning to swords being a side arm: swords were not even the preferred sidearm to deal with armored opponents, that honor went to daggers, which were better in a grapple and could be more easily used to penetrate gaps and visors. Rondel dagger and other specialised daggers were designed with thick (but narrow) blades for maximum stiffness and to allow them to get into gaps more effectively.

It is also worth noting that not all opponents on a field of battle would be well armored - while a polearm or spear might be more ideal for dealing with the highly armored, wealthier opponents on a battle field, a sword is more than sufficient for dealing with the less armored, less wealthy men opposing you. As a result, concurrent with the development of more thrust-centric weapons, we still see dedicated cutting swords being developed and used, including things like the type 1a falchion (of the Elmslie typology), which were specialised to cut through less armored foes using things like padded gambesons and jacks.

Even a relatively well armored, middle income soldier is likely to have some areas that are less than ideally protected, which provide an opportunity to make use of a sword blade. For the more armoured opponents, things like hammers, maces and pole weapons were indeed used.

The basic point of a sword is the sharp bit at the end. Joking aside, swords are useful because they can both stab like a spear and cut like a axe. In the Early Middle Ages, when metal armour was fairly rare, swords were very effective, though costly to manufacture. By the High Middle Ages, swords were cheaper and easier to produce but, of course, so was metal armour, which eventually evolved into full plate armour. As you point out, blunt weapons such as maces and hammers are more effective against metal armour, in that they transfer a lot more force through the armour. That doesn't mean, however, that a sword is useless. A sword can still transfer a lot of force through armour, especially if that armour is not carefully designed to deflect swords. There's also the fact that, while a hammer can be used knock someone down, you often need something slim and pointy to slip through a gap in the armour and finish the job. By the 15th century, sword-points were tapered to help with this. By this point swords were generally a secondary weapon, but still very common. A sword wasn't the most effective weapon but it was arguably the most versatile. It had a longer reach than a hammer and was better for bludgeoning than a spear was. It was easier to slip a dagger through a gap in armour, but you might not have time to draw your dagger. Perhaps most importantly, the sword is an excellent weapon for parrying and defensive swings. But we must also remember that, while the richest men on a 15th century battlefield would be encased in plate, most people wouldn't. Most would have armour that only protected parts of their body, making them vulnerable to cuts and thrusts from swords.

Sources

Mike Loades, Swords and Swordsmen

George Goodwin, Fatal Colours: Towton, 1461

It seems like swords are commonly associated with the medieval period within Europe and it doesn't really make much sense to me.

Swords were not just a Medieval thing, but were used long before then, and long after then (with swords being intended for use on the battlefield into the 20th century, with early 20th century cavalry swords and even infantry swords such as the Chinese dadao). A large part of the popularity of the Medieval sword is due to it already having been a popular weapon.

Just as was the case both before and after the Medieval period, the sword was usually a secondary weapon, with the main weapons in battle being bows/crossbows/guns and spears and other polearms. Most of these soldiers, at least by the later Medieval period (when swords were common and affordable), would have carried a sword as a sidearm. This made swords very common military weapons - if not only most spearmen, but also most archers, crossbowmen, and gunners carried them, they would be more common than even the spear.

There were other competing weapons, such as axes and maces (and large knives, if you distinguish them from swords). Swords have some advantages over these. They can be easily worn scabbarded, which makes them readily available in an emergency. A sword is also typically longer than a one-handed axe or mace, providing more reach in battle. A sword is less specialised than a mace, and as a sharp cutting weapon, can deliver plenty of damage to unarmoured opponents. A sword can be more agile than an axe or mace of similar weight.

if most of the people you are fighting are armored why not use maces instead?

We see rather more maces during the late Medieval period than earlier or later. It seems that some people did choose to use maces. A mace does have the advantage of a weight distribution that more readily lets it deliver blunt impact force than a sword, and construction that makes it unlikely to be damaging by hard contact with armour. However, a mace is no panacea against armour, and helmets and breastplates that are designed to keep high-energy crossbow bolts out will provide good protection against maces. It is not just a matter of swinging a mace against an armoured opponent and being guaranteed a disabling or killing blow.

Swords, while not being capable of cutting through metal armour worthy of the name, are not helpless against armour. Typically, armour has gaps, and swords can be used against these gaps. This varies from trying to thrust a sword point through a narrow vision slot in a visor to simple hitting an unprotected face or backs of legs (one blow of this type, to the unarmoured back of the legs, is famously know as the "coup de Jarnac" after its use in an armoured judicial duel in 1547). Some swords were even designed with this kind of use in mind, such as needle-pointed longswords, which sacrifice some cutting capability in exchange for stiff points that can be driven into gaps in armour. u/darthturtle3 discussed sword techniques against armoured opponents in https://www.reddit.com/r/AskHistorians/comments/a0tonl/are_swords_even_effective_against_plated_armors/

Further, not all armour was metal, and swords could be effective against textile armours.

I discussed the popularity of sword vs mace in https://www.reddit.com/r/AskHistorians/comments/bt56r6/why_were_swords_more_popular_than_maces_in_the/