There’s one simple answer, and other, side-benefits.
Canonical has an “all snap” desktop platform based on Ubuntu Core, which doesn’t support installing deb packages on the host OS. A stock Ubuntu Core-based desktop cannot install either the steam.deb
from Valve or the steam-installer.deb
from the Ubuntu repository. It’s as simple as that.
Side benefits:
Some people prefer to use older versions of Ubuntu. You’d be amazed how many 16.04 users there are! These (significant number) of 22.04 and older releases are getting fewer updates to critical game-related packages - such as mesa. Indeed, it’s technically challenging and time-consuming for engineers to backport drivers to one supported older LTS release, let alone multiple releases.
Having a snap package that can bundle not only the Steam client and runtime but also the necessary GPU drivers, controller support, and other requirements is a benefit for users who can’t or won’t upgrade the OS.
Also, minor quibble.
“huge amount of developers time”
The steam snap has 324 commits with most of the work being done by two developers.
Now, granted some of the work done to make the steam snap “work” will be found elsewhere, such as in the snapd steam_support interface, but even that only has a single page of commits, over three years.
It is not exactly a massive code churn with a “huge” number of developers. Maintaining a snap - even one as complex as the Steam snap, isn’t a tremendous amount of work, to be fair. It’s not zero, but it’s not a room full of developers.
For Valve, Ubuntu isn’t their primary (or even secondary) target platform for Steam. If Canonical steps up to maintain a package, be attentive to bugs, and enable users on various Ubuntu releases to play games with the latest hardware support, that seems like a benefit for those users to me.