Memory leaks very often don't fail loudly. Especially if they are slower leaks which don't immediately break the application.

A lot of the memory problems that you can see without a GC are hard to find and diagnose. Use after free, for example, is very often safe. It only crashes or causes problems sometimes. Same for double free. And they are hard to diagnose because the problems they do create are often observed at a distance. Use after free will silently corrupt some bit of memory somewhere else, what trips up on it might be completely unrelated.

It's the opposite of failing loudly.