The video explains why. The goal isn't small, it's minimal.

By pursuing small at the expense of compatibility we got things like musl libc (which has tons of compat issues).

If all we wanted was small we could have started from musl libc and unpacked alpine packages the way we unpack debs.

There are more minimalistic (and smaller!) and more compatible images out there though. So, we got the goal of distroless, but its good execution is yet to be seen!