To add some context, the follow_symlinks parameter was added to os.stat() after adding support of *at() functions (like openat() and fstatat()). Since both C functions stat() and lstat() are superseded by fstatat(), the latter was exposed at Python level as adding new keyword-only parameters to os.stat(). This allowed to avoid significant increasing the number of functions in the os module.
Since there is no function that supersedes both posix_spawn() and posix_spawnp(), this may be an argument for exposing them as separate functions at Python level. Although this argument is not very strong.