Mastodon is a microblogging platform so it somewhat makes sense for it to enforce a character limit. That being said, I agree that 500 characters is not a lot, especially for what GOS does.

Well, there are Mastodon forks, like glitch-soc or hometown, which do indeed have a modifiable character limit. And it seems that migrating to one isn't too difficult.
So there's a solution. Either GOS is unaware of it, or they chose not to go this route.

CC: @GrapheneOS@grapheneos.social