It does, ceteris paribus [1]. But blocking people from exiting a position you got them into, particularly something volatile and almost self-identifying as a bubble asset, is a lot more problematic than blocking people from opening new positions.

[1] The OCC (options) nets. If you have a large collateral requirement in a position and then reduce the size of that position with offsetting contracts, your collateral requirement goes down. I don't remember if the DTCC (stock and other things) does this.