More than just 1 aspect probably.
I agree with TC it was probably a blend of users mo longer putting up with being attacked by other users, and those users finding another online space. Discord is probably a large contributing factor, but more broadly the shift in the internet away from forums. As older members leave new people are not looking for a place like this.
I don't think the attack part is true or SC would have died a long time ago but I could be wrong