While it's true that Steam has a lot of critical mass, there are several viable alternatives for distribution in a vacuum (whether publishers and developers use them or not doesn't mean they aren't there). In addition to the EGS and Itch you also have GOG (which has a huge catalogue and is highly curated), and the Humble Store is still around even though sadly it has mostly become a Steam storefront these days. Add to that other publisher-specific distribution platforms and the landscape is hardly as bereft of choice as the smartphone/tablet app distribution ecossystem.

Note: I do wish all of these people's official clients supported Linux.