From my understanding the CS:GO matchmaking basically ranks how likely of a cheater it thinks you are, and matches you with people of a similar ranking. If you're queuing with people that are bragging about blatantly cheating you're probably in the "likely cheater" group.

This is all really just anecdotes, but here's my counter anecdote. I play csgo on and off with friends. None of us have ever cheated in csgo (or any other competitive online game for that matter). I'd say we get about 1 obvious cheater every 50 games, with 2-3 less obvious "maybe they're using wallhacks" as well. This is significantly improved from 3-4 years ago where we got a cheater once every 4-5 games.