There are other good reasons to not support older systems, beyond commercial interests.

Every additional system that is supported comes with a cost of time and effort. When the system is rare (SPARC), continuing to support it doesnt make sense, especially when that time and effort can be put towards maintaining other more common systems.

Also, supporting older systems can hold back new technology. Most Linux distros are built with an ancient minimum x86 version, which means that many of the modern CPUs aren't being optimised for. Its good for compatibility, but it is holding back new systems. Every Ubuntu/fedora/etc release their respective steering committees will usually have a discussion about dropping older CPU support. Gentoo at least has a solution for that, because everything is recompiled for the specific system.

IMO, if their system is so resource constrained that 1.5mb is too much to bear, they're well into the "holding everyone else back" territory, 128GB SSDs are 40AUD, which is two big Mac meals. And if they are on SPARC, thats well into the rarity territory, the last SPARC CPU was released in 2017, and they were never common for consumer PCs.

There is a difference between "planned obsolecence" and actual obsolecence, and this case feels like the later.