How are we supposed to know the exact reason?

There are several possible reasons, such as cheating, toxic behavior, smurfing, etc.

The account has a GAME ban

https://psteamcommunity.yuanyoumao.com/discussions/forum/9/620712364027233611/

Game bans have nothing to do with VAC or this forum

Users are responsible for the security of the account and all that happens on it

引用自 Dark_5ide：

Why did I get a VAC block for the game Call of Duty???

1 game ban on record | Info
0 day(s) since last ban

you dont have a vacban. Call of duty uses a different anti cheat system. Go to your profile and click on the info button. gameban have nothing to do with vac forums