Just personal experience playing with unusual hardware platforms over the last couple of decades. Usually the download pages for the respective distros list all the CPU architectures they support Ubuntu needs a little more digging to locate their non-x86 downloads (which I believe are only ARM and POWER8). There used to be some ropy support for SPARC but that was nearly a decade ago.
These are exotic platforms, therefore go for a distribution that supports them.
I did. Again I feel the need to reiterate that my point was Ubuntu isn't the only multi-platform distro (despite the GP's claim). The rest of my post was exampling that point.