It feels like Oda just walked through the storyline in his head and added a scabbard for every minor thing he needed instead of trying to limit his numbers.
We can't introduce Momo by himself, so of course he needs a Scabbard to himself. Even though Kinemon was inevitably gonna overshadow Momo back then and definitely attracted more of the fans interested in their plotline than Momo himself.
We can't rationalize Kinemon and Momo being OK with a detour to Dressrosa, so we better put a Scabbard there for them to look for.
We need Jack to attack the minks so let's make it because he's hunting down a Scabbard there.
The minks need to be able to fend off Jack for awhile, so let's make them have 2 leaders that alternate day and night and let's make them BOTH Scabbards to help push the mink connection for Wano later.
We need a replacement for Izo since he ended up leaving and we can't have Oden's death without a full count so let's give him a sibling who'll be that replacement Scabbard.
Gotta make Oden look cool by beating up some big gang leader, and it'd be even cooler to have him recruit the guy after, so let's make that one of his Scabbards.
We need someone to save Hiyori from the burning castle, so let's add a fishman and make him a Scabbard.
Then we need Hiyori to end up working as a courtesan in the city to work her way up to Orochi, so the fishman has to go away. But I can't let her do that as a kid without some protection, so I'll make another Scabbard that also goes undercover to protect her.
Let's make sure Izo returns for the big battle, so gotta make sure there's a traitor scabbard who definitely can't be redeemed to switch sides back or anything positive. Guess I'll make the traitor related to Orochi.
Some of it works, but it's been talked to death how easy it would be to combine and reduce the Scabbard count. But sadly, I guess it was decided that Oden wouldn't look cool enough if he was only holding 4 or 5 people up and out of the boiling pot.