It would be harder maintaining a large collection of software outside of one of the major Linux distros. Debian/kFreeBSD might have a chance thanks to the GNU userland, but the archive is less well supported than with the Linux kernel.
Quite the opposite. This isn't about the userland, it's about the kernel. The linux kernel is where the high-performance cluster computing advances have been. The GNU userland is just a clone of the BSD userland, nothing special there. Moreover, FreeBSD and OpenBSD's packages are diverse, well-maintained, and current. But neither OS's userland nor any of their packaging systems have anything to do with high-performance cluster computing.
