Even if they could, it wouldn't let them play switch games better. It doesn't solve the clear problem here that is the super technically minded people wanting to play Mario and Zelda in 4k/60.
"Open" doesn't mean "open source" although in the case of the Steam Deck, it is both (not including the Steam application, but as I mentioned you can use the Steam Deck for whatever you want including removing the Steam application, so it's not a requirement or a blocker. I know someone who installed their own Bazzite flavor that has Steam removed and only uses Lutris to install GOG games).
Also Steam Store's requirements are only for games listed in their store. As has been mentioned, this is not a requirement for running on the Steam Deck. This is in sharp contrast to Nintendo.
Given all that this doesn't feel like a plea to let people publish their games. Just a thinly veiled port begging.