This is a misconception. Apple has something like 90% of the market share of all computer shipments above $1,000 in cost. Those shipments dwarf custom builds. Also, you can visit the Steam hardware survey, expensive ($1,000+) PC builds are quite rare, actually maybe only about 10% of the Steam audience, which neatly matches the expectations for who owns the premium end of the market.

Not sure why I’m being downvoted. Anyone can easily verify what I’m saying by visiting the Steam hardware survey. I know that this does not match the expectations of HN readers!