This smacks of 'Canonical realizes it has to shoehorn in all popular apps to make Snap capable of competing with Flatpak'. Steam is, for better or worse, one of the most popular applications in the world right now.
Right now, Canonical is doing the same thing Sony does whenever they try to float a new media format: Beg, Borrow, Steal, Blackmail, Bribe, and Bully anyone they can into using it to try to maintain some control over the future of that media. Also, right now, they're in the same place that Sony WAS in when VHS hit the market. Betamax/Snap was/is failing not just for technical reasons, but because it's bad for everyone around for one bully to control an entire market.