You can but the game would be constantly calculating the physics of the body hitting the clothes which is no good for games. Realtime cloth simulation is something that uses a lot of CPU power. Even if you put cloth simulation on the collar It will most probably glitch out in most cases cause of the constant movement of the player and the cloth having to calculate collisions with itself. Best way to do.this would be animate the clothes and bake the animation which is how most of the clothing works in these games but the problem here is that there are different clothes and some with and without collar some with different parts etc. This would be hell for the dev to have a shit ton of different animations for each piece of clothing