What happened with VAC ???

Long story short - I had my times with CS from 2014 to 2017. Now I came back as you may call 'noob'. I currently don't have prime status, and every second game I play there are cheaters... 1 on each team, 2 on each team, even full opponent team. What happened with the VAC system? I remember it working better. Now they don't even try to hide the cheats... And a month back I had a good night session with myself. I was on shrooms and xtc, put on some music in browser, and played arms race - I kinda started to 1tap heads as a mf, i guess it was shrooms or both... Anyways - game threw me out of lobby and warned me that VAC system has detected something wrong with my play... I thought to myself - damn, i got so high they think I am aimbotting. Why it does not happen to all the cheaters I see everyday? And if I would decide to buy Prime status, is there a guarantee to play without them?