As far as I can tell the fedora guys wrote libhawkey and dnf to reach some sort of middle ground, as switching to zypper would have implied breaking everything (i.e. all the scripts admins use, rewriting parts of anaconda, etc). The compatibility is not perfect, and in fact a fair amount of people complained (see some discussion on phoronix). As far as the parent post is concerned, to switch to apt would imply switching to deb, which would be a massive change. RPM is simply too different, both in positive (the possibility of changing target directory and of rolling back) and in negative (dependency specification is still rudimental compared to .deb, see https://www.youtube.com/watch?v=FNwNF19oFqM). And as rwmj14 said, libsolv is better.