Abseil has a btree based hash map and it performs much better. I think it maintains the same constrains(iterator invalidation/exception safety...) as std::unordered_map.

The issue is that the implementors won't change their implementation of unordered_map as it's an ABI break, to say it simply. It could be better. But also, there are other tools like flat maps/open addressing that are not done in the std library.