The NetBSD kernel still has support for a.out. On BSD, a.out is something simpler than ELF that works without any problems.^1 On Linux, a.out may have caused problems when building shared libraries thus motivating the switch to ELF.^2
1. ELF is OK, but times have changed since ELF was created. The same constraints no longer exist. Personally, I prefer static binaries and can afford the space for them. It is good to have options for people who prefer shared libraries as well as those who prefer static binaries.
1. ELF is OK, but times have changed since ELF was created. The same constraints no longer exist. Personally, I prefer static binaries and can afford the space for them. It is good to have options for people who prefer shared libraries as well as those who prefer static binaries.
2. https://people.freebsd.org/~nik/advocacy/myths.html