Unfortunately the period of time during which humans carried swords happens to cover all of human history, so my answer must necessarily be in brief.

Swords, despite the mythology that has risen around them, tended to be sidearms. Spears were often used before swords came out, and when they did come out they were typically drawn from the hip. Specifically, we have examples of scabbards from samurai from multiple periods: ancient Greeks, Romans, various Middle Eastern civilizations, various Chinese dynasties, and Medieval Europe. I am not aware of any that were designed to be drawn from the back. In fact, Edo samurai carried two swords with them wherever they went, and only on their hip.

Phalanx armies in particular tended to be quite regular with their equipment, and they would often have hip-drawn short swords designed for use when a spear breaks or is otherwise lost. Medieval knights would usually carry an arming sword on their hip, though they might have a larger sword designed for mounted combat sheathed in their saddle, but that would still be located in front of them. It is entirely possible that marching soldiers would carry larger swords on their backs, but the only imagery we have shows them carrying their weapons in their hands or in carts. Besides which, it is very unlikely that back sheaths would have been designed to accommodate marches.

The sword-on-the-back trope probably has its roots in the oversized swords we see in much of media. When artists (both Eastern and Western) and prop designers created exceptionally large swords, out of proportion with what would actually have been used, it only made sense to carry them on your back as they were far too unwieldy to be on the hip.

As I've understood it, strapping a sword across your back is extremely impractical. It makes it harder to draw, take longer to draw, and makes you more vulnerable while drawing it. With a hip sheathed sword you're assuming a defensive position as you draw your sword. It's quicker. You typically have one arm that you can move freely. It's just all around better.

There is one instance where a shoulder sheathed sword becomes practical. And that's when you've got a short guy wielding a long (hand and a half (bastard) or two hand (great)) sword. But even then, only if it would be dragging on the ground.

As these weapons were not a popular choice for actual combat (bastard swords would be used. But shields were very important to your hand to hand fighter, so great swords were less popular), its likely this style of sheathes were more decorative or ceremonial than anything else. Kind of like how we use ceremonial rifles in modern military displays. They're obsolete for combat purposes, but look much better than what's practical.