[tialaramex]

The overwhelming C++ priority beating both safety and performance, often to the consternation of the performance people, is backwards compatibility with dusty archaic code. If it was written by somebody whose funeral was last century, WG21 thinks it's important that it still compiles in your C++ 23 compiler whenever you get one of those. Not crucial. Not so that they actually defined the language sensibly to avoid compatibility problems, but important enough to trump mere performance or safety concerns.

Last century move didn't exist. The terrible C++ move (which is basically an actual "destructive move" plus a default create step) was invented for C++ 11 which was, as the name suggests, standardised only in 2011.

So back then everybody is using copy assignment semantics. Your compiler might be smart enough, especially for trivial cases, to spot the cheap way to deliver the required semantics, but it might not especially as things get tricky (e.g. a std::vector of std::list) and semantically it's definitely a copy, not a move.

As a result the "non-move" that you're astonished by is how all C++ code last century was written, the semantics you're just assuming as necessary didn't even exist in ISO C++ 98 and it is considered important that such code still works.