I'll mention a significant case that doesn't have to do with allocation. Large graph-like data structures (lots of small nodes linked by reference) are effectively prohibited entirely by the GC. They make every marking phase take much too long, until whenever time the whole thing gets promoted into the long-lived generation. A mainstream runtime having such an impactful opinion about my data structures (not alloc patterns) is something I just find deeply offensive. Imagine if C++ programs stuttered because you had too many pointers!

They could have avoided that whole problem by providing an API like DontCollectThisRoot, but instead they (and a lot of programmers) chose to pretend the GC was good enough to treat like a black box.