Of course it does, seccomp, developed way before pledge :))

And where is seccomp used (by default)?

Chrome and Firefox both use seccomp by default on Linux.

OpenBSD has around 500 programs with pledge support in base.

edit: and this number does not even include the ports available with pledge support, among others chromium.. and the fact that they were capable of adding pledge support this quickly says a lot, imho, about the implementation differences between libseccomp and pledge.

Also, pledge is everywhere. Seppconf, not. And SeLinux just in few distros.

Pledge is instrinsic. You have it right from the beggining with C and Perl. And it's straightforward to use.

Not the same approach.