There are multiple reasons for the Steam forum toxicity. The barrier of entry is super low, you can post as long as you have a Steam account (which is prettty much everyone). You can also earn points when someone grant you an "award", that you can use in a shop for Steam profile assets. That led to what is called "clown farming" where people are posting the most silly things just to earn as much clown reactions as possible. The moderation pretty much doesn't exist there too, so outrage threads can last for months before being locked.
If you like a video game, the Steam forums really isn't worth your time.
