Because even though M&B has crouch animations and a crouch walk, they're not very good. I'd have to create a stationary, crouch walk, and likely a crouch attack animation for all or most of the weapon types. That's really a lot of work and it's hard to say it will have any meaningful effects on gameplay, especially when there's no guarantee that I can make the animations look good simply by keyframing. For melee, you can crouch behind objects, but that's about the only use you can get out of it. There aren't even very many maps that you could find a single use for this. For ranged, this only serves as a tool that would better keep you hidden, but it still won't have very many applicable uses.