That's not true at all. Plenty of developers sell through the Epic Store (having development funded by Epic), or GOG, or the Humble store, or on Itch.io, or even via microsoft store. There are abundant ways to fund a project on PC precisely because it isn't a walled garden. Sure Steam has massive dominance, but that is arguably because of the relatively open nature of steam itself. Valve don't have or seek a monopoly on distribution.