You could make an ATX form factor ARM or RISC-V machine with a lot of processing power and run Linux on it, but who would buy it and for what? That question is why no one makes such a thing.

The same people who buy ATX form factor x86? The only thing making these platforms different is software support, which is getting better for RISC-V everyday. You wouldn’t buy a RISC-V computer today for high performance gaming or scientific computing, but it definitely works as a general purpose machine (web browsing, office apps, watching videos, etc.) This year shouldn’t see much progress in hardware since RVA23 just came out (maybe some RVA22 + V), but you can expect some nice things to come out 2026-2027 since now you have all you need to build a competent RISC-V CPU.