When I worked at Apple they were the first resort as they were usually cheaper to iterate with (no recompilation, lower overhead, etc), but ASAN has only gotten better & was the primary focus. I agree that maybe jemalloc might be a good drop-in replacement, but it just might not be a priority for the libc maintainers. Lots of low hanging fruit can be missed for very long periods of time because you have to pick what to focus on.

GWP ASAN from TCMalloc might be the better direction for runtime support for memory corruption from malloc as it gives a lot of ASAN-like protection with an electric fence-like performance profile (& can be turned on/off at runtime).