This is a feature existing in cheat program, the cheater just have to press a key and he got teleported out of bounds.
https://www.youtube.com/watch?v=PxIMeWf6GGo
Maybe because there is an exploit in the code of the game originally so they can use that (it was fixed in CSGO but they found a way to make it work again from what i understood), but yes i agree with you it happens very very often since last stand update this really need a fix. Basically it happened to me only once in a few month in the begining of 2020 but now it is almost every 5 games.
I have the nobhop plugin too but i did not modify the cvar you have mentionned (and using SM 1.11 dev), but this seems to be exploited on official servers too so i don't know.
I will open an issue on Valve github but honestly when i see all the isues not resolved, i don't get my hopes too high.