Microsoft's design philosophy in any of their products has gone from well organized menus to relying instead on a search bar. Copilot is a further addition to that design, with yet more pushes to never use a menu, but instead just tell it what you want and have it spit it back out. They want everything you make to go on OneDrive as well, so it can also be indexed this way. Teams works the same way. The big search bar at the top is unavoidable.

Windows search is complete garbage, which you might think is a counterpoint, but instead it's just that they only put work into having it serve results for cloud-indexed items or web results.

It literally keeps every single conversation you've ever had in a big long list on the left,

Not all of them, actually. I regularly have to use the search function to find chats/groups I haven't used in a bit. The most organization you can do is the dozen pinned threads they let you have.

I believe they will never allow users to delete entire chats like that because it will cause mass panic for users and managers, particularly. You already have users doing dumb shit like deleting files accidentally. And more than that, you’ll have managers getting upset that users may be doing it on purpose like “omg I never saw that message! 😱 “

Deleting your own stuff is easy and okayed because it’s not an easy process and it involves multiple steps.

with absolutely no way to organize it, categorize it, order it, or in any way manage it other than deleting history

But you can pin any chat and you can reorder any pinned chat (and maybe even non-pinned ones - I haven't checked).