They could’ve been Robinhood (and avoided someone buying the one they stole from) if they completely emptied that one into several others.

Maybe not these days, but it used to exist. Geocities comes to mind.

They only added threading because teams added it. I hated it when it launched. Now I find it kinda useful, but if they were deeply nested things would undoubtedly get lost. Either way I don’t think it’s a technical limitations so much as it’s a product design choice.