My reasoning: character count isn't about content but about form.
And practically, while your fediverse reading program might not be able to understand a post well enough to see what the content is about, and give you a warning, it can easily detect character count and do something you'd like if the count is too large.
If you want to skip all posts above 500 characters or whatever, it would be trivial to program a client to do that. It's a UI issue.
@jrp I'm with you, personally, but then I'd say with good UI design there's room for all of us here, for different users to tailor their experiences to their personal preferences.