Assassin Creed Logic

If you’ve ever played the Assassins Creed series you’re well aware of how many different possibilities  there are as far as how you can get around. You can run, jump, roll, climb but there is one thing you can’t do and that’s crouch. Why is this? We still haven’t figured that out yet.  I imagine It wouldn’t be that hard to implant which is why it confuses us.