They will not tell you why you got game banned, but there is a nice little info button on your profile next to the red GAME BAN letters that has a lot of info.
in short it can be for many reasons, like cheating or match making or smurfing or toxic behavior.

Originally posted by 蔡阿:

How?
whats the reason i got banned?

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

let us guess, the ban is for CS2. then it can be given for one of a few things. and its permanent

gameban cs2 - https://steamhost.cn/help_steampowered_com/en/faqs/view/4E54-0B96-D0A4-1557

Why are game bans issued?
Game bans in Counter-Strike 2 are issued when a player attempts to circumvent or interfere with game systems to the detriment of others.

Examples include:
Cheating.
Manipulation of matchmaking rank by deranking or falsely increasing your Skill Group or Counter-Strike Rating.
Botting and/or automation.
Intentionally interfering with the normal operation of game servers or other players.
Game Bans for all of the above are not removed by Steam Support.

Can you tell me why I was game banned?
No. We do not disclose the reason for your game ban.

Whether you were using cheat software, automating matchmaking, or abusing matchmaking the reason a game ban was issued is not shared with users.

Can I appeal my game ban?
No. Game bans cannot be appealed and are not removed from accounts.

I was not using my account when it was game banned. Can the ban be removed?
No. Regardless of who was using the account at the time the ban was issued, game bans are permanent and are not removed.

Can I move my Counter-Strike 2 items to a different account?
No. Counter-Strike 2 items cannot be moved from a game banned account to a different account.

Can I upload content to the Counter-Strike 2 Workshop and Community with a Counter-Strike 2 game ban?
No. You cannot upload new content, such as guides, artwork, or Workshop items to the Counter-Strike 2 Community if you have been game banned.

Can I vote on Counter-Strike 2 Steam Workshop content with a Counter-Strike 2 game ban?
No. Counter-Strike 2 game bans prevent voting within the Counter-Strike 2 Workshop.