This game would feel pretty empty without them!
I dunno. Not many weapons had them. Daggers, definnitely. Sideswords (in its broadest sense, meaning basically anything bigger than a dagger but still meant primarily for 1-hand use), as the name implies, definitely. Longswords, maybe, maybe not. A blade 1m long from tip to crossguards would be hard for a person of average medieval (or even modern) stature to wear at the side unless on a horse, not to mention the 2-handed hilt above the belt poking into the armpit. And unless the person's arm was longer than the blade (which is highly doubtful), he couldn't draw it without grasping the blade with the left hand. Nothing fast there. I'm not even going to bother with the Hollywood back-mounted thing. Greatswords, the even bigger zweihanders, maces, flails, and axes and pole arms, definitely not. Most of those were battlefield weapons anyway, intended for use en masse, not as personal defense weapons.
And even for weapons that COULD have a sheath/scabbard, the sheath/scabbard would have to be paired with a specific weapon. Remember, this is all pre-industrial so everything is hand-made and no 2 things are identical even if forged by the same smith. The sheath/scabbard that fits Broadsword A almost certainly won't fit Broadsword B. So if you found Broadsword B by itself, naked in a bucket, then you have no sheath for it. Ever. Unless you go to some NPC vendor and pay to have one custom-made for it, and then it won't fit any other sword. Now, if you buy a small sword from a vendor, I would assume it would come with a sheath, but that sheath would only fit that particular sword.
This all means that scabbards and sheaths would have to be separate items of equipment just like armor, and would have to be paired with a specific weapon. And given that only a minority of weapons in the game (essentially only the smaller blades that are either bought at stores or, in some cases, looted scabbared/sheath and all from corspes) would likely come with matching sheaths/scabbards anyway, this sounds like implementing a lot of overhead for very little gameplay value. Therefore, I'm totally fine with not having scabbards/sheaths in the game.