Its a fools errand to go on a "free" platform and complain about corporate presence. If you are not paying, then those corporate bodies are.
I have (and I imagine most people over 25 have) used plenty of forums, wikis, and other social medias that are free as in beer, hosted by some guy with a computer in his garage, with technology from decades ago
The better ones of them asked you to pay if you wanted to be able to post video/large images. In most of those spaces, corporate was nowhere to be seen. Sometimes they used banner ads, but often, nothing at all but a single person's internet bill was the entire cost of the site. Such places still exist, and are good.
The internet is getting worse by the day. It's been getting worse for so long, that people are starting to wax lyrical about how it can't possibly work any other way, this is just the natural state of things.
Of course, if you absolutely must mindlessly go to the dopamine trough and get your fix of algorithmic profit engagement, then yes, you will end up in places that relentlessly seek profit via one form of another. But if you filter even a little bit for quality, you'll end up somewhere else.
The world is not better when everyone is exactly the same, it's better when everyone has a place they feel welcome. For some people they enjoy reddit or discord, others don't. There's nothing wrong with someone preferring something made out of passion, rather than something made to make more money.
Yes, the problem is that the overwhelming majority of people using sites like Reddit or Discord are not choosing it. They are there because it has become their only alternative.
And it has become their only alternative because all these hobbyist forums can only exist when they are serving some tiny, exclusive priviledge few. If they grow too much, they either will crumble or will find themselves becoming a "professional" service with people on payroll and revenue targets.
I'm not sure I agree with this, but it does fit the pattern. Auto forums are an example of this working. But I wouldn't call that a privileged few, would you?