it's not "another thing", it means that your community forum lives on reddit (or whoever's) sufferance, and is subject to some corporation's capricious and arbitrary whims.
this comment brings up a good concrete example: https://news.ycombinator.com/item?id=49293553
This is a better comment on the same page: https://news.ycombinator.com/item?id=49296018
Basically: "everyone has a different idea about what the Old Web™ was depending on when they first started using the internet, and when the community they liked was discontinued or changed"
that's a good comment for sure, but it doesn't address what I was talking about - specifically, in the "old internet" it was a lot commoner for a community to own its online spaces, usually by virtue of having one or two technically minded members who volunteered to run the infrastructure, and thanks to a lot of the required software being open source. sure, it's nice that anyone can just create a subreddit or facebook group now with no technical knowledge required, but there are definite ways in which living in someone else's space shapes your experience for the worse.