Why does this matter? If popular OS distributions consistently target ARM-based CPUs, with a sufficient number of packages (esp. development-support-related) working on them, then who cares about fragmentation? An organization could buy systems with ARM chips and software will basically "just work".
Same argument for consumer PCs, although there you have the MS Windows issue I guess.
The more fragmented your community, the harder it is for software to work consistently across all of them. Intel vs AMD has plenty of obscure issues (see "rr" project, and all the issues getting that debugging tool to work on AMD even though it has the same instruction set).
Sound, WiFi, Ethernet, southbridges, northbridges, PCIe roots. You know, standard compatibility issues that having a ton of SKUs just naturally makes more difficult. Having a "line" of southbridges / consistent motherboards does wonders for compatibility (fix the BIOS/UEFI bug in one motherboard, fix it for all) in Intel/AMD world.
But just as AMD has AMD-specific motherboard bugs, and Intel has Intel-specific motherboard bugs... I'd expect Graviton to have its share of bugs that are inconsistent with Apple M1 or Ampere Altra.
Why does this matter? If popular OS distributions consistently target ARM-based CPUs, with a sufficient number of packages (esp. development-support-related) working on them, then who cares about fragmentation? An organization could buy systems with ARM chips and software will basically "just work".
Same argument for consumer PCs, although there you have the MS Windows issue I guess.