Some of this is just knowing from experience, by the time C++ programmers knew they wanted the destructive move assignment semantic at the turn of the century they already had large codebases which relied on C++ copy assignment, so, too bad. It took a significant extra effort to land C++ 11 move semantics, which are still less useful but also have worse ergonomics. Whereas Rust knew it wanted the destructive move so, that's just how everything works in Rust.

But there are a bunch of unforced errors in C++ design beyond that. Default implicit conversion is a choice and a mistake. Multiple inheritance is a mistake, Stroustrup even says he did it because it was easy, which is exactly the same cause as Hoare's NULL. Choosing "All correct programs compile" (the other option was "No incorrect programs compile", you can't have both, see Henry Rice's PhD thesis) was a mistake. My favourite bad default in C++ is atomic memory ordering. The nasty trick here was that picking a default was the mistake, it's not that they picked the wrong one but that they picked a default at all. C++ programmers end up writing code which doesn't specify the ordering even though the ordering was their only important decision.