There is a technical cost to more inventory, even yoship even explained it years ago. As a programmer myself I'll explain a little bit.

If you add say another 50 slots to your inventory that means those 50 items have to keep "following" you everywhere, which is a server cost. It can affect performance, and probably instances the most since those servers track you much more because of battle mechanics than say in your housing area.

So with that in-mind, it's way easier to add more glamour drawer slots because they are only in the big cities in the inn or GC room. Those slots aren't following you everywhere. Saddlebag is almost the same concept where you can use it almost anywhere, but they do not follow you on instance servers.

Tokens are a smaller cost, because that's another set of code that has to follow the character. Like it's a waste of resources to have the game track how many Susano tokens years later when you probably stopped caring two years ago. Beast tribes are always relevant and they used up that resource.

Look in the 6.0 keynote, YoshiP said they were taking back 10 belt slots for reserve. So that means current capacity they could re-allocate elsewhere or use it for something else.