Because that was alpha version of an engine and it is far easier to ship demo to three SKUs than to a limitless permutations of PCs(and you shouldn't forget that most PCs won't be able to run this with adequate performance). Matrix Demo is available as UE5 project right now and you can download it and build it(it weighs 90 gigs though).

Corporate captive consumer strategy approach.

Which PC hardware setup?

There is a reason why game studios love consoles so much.

It is mostly the same during 5 years.