It's not a matter of challenging Steam but of convenience.
Much like streaming, everyone prefers having their content on a single app/platform/whatever. Plus Steam has some other benefits like Big Picture that nobody else has.
Besides data sovereignty and user manipulation, the relationship between competition and convenience seems like the biggest issue in tech now. And there are no real solutions. It‘s obvious why tech is so consolidated. Marginal cost of growth is pretty much zero. 2 to 3 platform for a given use case might be the most „efficient“.
Chances are that quite a few of the new streaming services will disappear/consolidate soon enough.
The catch being that it only applies to movie purchases by participating studios. No rentals, subscription based streaming, or TV shows.
But imagine if that's how other services worked. One can always dream.
A tv series should be distributed on all platforms, rather than just HBO or Neflix or Hulu. Making exclusivity deals should be outlawed as anti-consumer.