It needs to be short - there is already a limit that worked well - why bikeshed it more?

A limit that worked well for who?

Almost every twitter/x post submitted to HN has people labelling their posts as "X of Y" threads, using images as text, or using pro account posts.

You can see it yourself: https://news.ycombinator.com/from?site=twitter.com Ive just looked at 30 and each of them exceed 280 chars by far.

It works well for microbloggers.

But clearly not the microbloggers on twitter/x, Bluesky, etc, who use the patterns I mentioned.

Those are definitionally not microbloggers. It's ok for a platform explicitly for microblogging to not cater to their macroblogging desires.

Definitionally not?

"Microblogs, for example on Twitter..." https://dictionary.cambridge.org/dictionary/english/microblo...

"Some popular social networks such as X (formerly Twitter), Threads, Tumblr, Mastodon, and Bluesky can be viewed as collections of microblogs." https://en.wikipedia.org/wiki/Microblogging

I think this is the opposite of bikeshedding, it's literally a core feature and constraint.