Earlier quoted context omitted.
They need to do that because, in some sense, they're competing with Gaming PCs, not really with Gaming consoles. Gaming consoles sell their consoles at a discounted price because they can recoup a lot of it when selling games. Steam can't have a markup on games because they share their marketplace with other PCs.
Steam has a very high markup compared to its competitors like Epic Games Store.
A interesting scenario would be to sell the hardware at cost, but include a 30% off ticket to the steam store (up to a few hundred dollars, in savings).