events are messages, server is sending those to players.
And player own game is triggered by those, player game could play specific sound or print messages in they game.
Example if you pre hook bomb_planted and block it, player not hear sound "Bomb is planted" and can't get message of it.
...if you want to block actual bomb plant, you need dig deeper in game code and find offset/signature of it.
After that, you can change or break game behavior.
There is cvar in some games to stop round end or objective happening.
Code:
"mp_ignore_round_win_conditions" = "0"
- Ignore conditions which would end the current round