I noticed that as well. I stopped visiting the Forza Forums long ago because it was a never-ending circlejerk of bickering about insert game, petty back and forth arguments, or just complete nonsense. I looked the other day because I got curious and what do you know? It hasn't changed one bit.
I won't name anyone specifically but it seems a few of the users consider this specific forum to be a bunch of Playground lackeys/defenders and it's a bad forum because of it. But if you had to ask me, it's more like this is a smaller collection of a few people that regularly play FH5 and still enjoy it for what it is. We all have issues with the game and that's fine too, but pretending the official Forums isn't one of the most toxic places of discussion for anything Forza related is laughable to me. Especially considering certain people there have openly admitted they just like bashing Turn 10/Playground Games/Microsoft for the fun of it. I mean, come on. One of the most active threads in the FH5 section is dedicated to trash talking the game and developers (you probably know the one). Don't get me wrong, some of the stuff they may complain about is justified, but at the same time, I've seen some of the most genuinely awful takes in regards to Forza ever conceived on the Forums over the years.
To me, it reads like, "OUR group is cooler and better than theirs". I wouldn't read into it much. I more or less made the switch from the Forums to GTPlanet because, in my opinion, it's just a more positive and friendly community. If you want to call that an echo chamber, sure man I don't really care. Maybe it's just me, but I prefer to not surround myself with overly negative and cynical people. It wears on you after a while and it's just not in me to be negative all the time, especially about a video game.
Mini rantathon over.