The main thing is that I don’t want to play with cheaters, and cheating is way more prevalent on PC. Thankfully, it seems pretty rare, but it does happen. I just don’t want to ever deal with it. There’s even stuff that might not be outright cheating, but doing things that weren’t really intended, such as creating macros to do a sequence of multiple actions with one button, etc. I know such things and straight up cheating can happen on console too, but it’s far less prevalent, and it’s far more risky/expensive, as you might get your console permabanned from Xbox Live.
I don’t care about M&K vs controller debate. I used a controller on Halo 5: Forge for PC and did well, and up until recently, I played Titanfall 2 on PC almost everyday during quarantine and I used an Xbox controller and would regularly finish in the top 3. Maybe it’s because of auto-aim, but in my experience, M&K adavantage only matters at high levels of play with all players being highly skilled. Otherwise (assuming decent proficiency with whatever your input method is), tactics and knowledge of maps and all the gameplay elements is far more important than a small advantage in twitch movements.