steamos holo was the codename for steamos 3. this project is called holo core because its the core for a new steamos version that will run on aarch64. the fact that its shipping on a vr device first is just a coincidence.

valves long term plan is a big transition from x86 to arm for all their hardware, steam frame is the first one because its made for streaming first so people wont complain if some pc vr games dont run on device.

the main reason is they dont want to stay locked to amd. intel is technically an option but they have a history of bad drivers and treating linux as a liability. arm gives a license to just about anyone so the market is wide open and valve can even make their own silicon if they feel like taking on a challenge.