I used to play Warhammer 40K. I got out for many reasons, notably, the price of models went from expensive to ridiculiously expensive (and have gone to outlandishly expensive since I left), the rules changed badly enough (TWICE!) I had to purchase an almost new army to stay competitive and last but not least, many of the players were jerks. While 40K is now on the 9th edition of its ruleset, Battletechs' core ruleset has stayed stable with a single rule change since this game was called Battledroids. The rules have expanded, but never rewritten.
The biggest reason was the players. This popped up in my social media feed the other day, but I saw it years ago. Meet Shooter and Wheels. The images explain the story.
While not impossible, it is very hard to Cheese a list like Wheels' in Battletech, namely a "Super-focused-Spearhead" that comes out of nowhere and can slice through any general list like a flamethrower through butter. I also like to think we have more polite players as well.