I don’t think that’s their goal at all. Otherwise we wouldn’t see any sequels released on PC, that would be a much better strategy for converting players to console. The only reason publishers require their own logins in games, at least for single-player titles, is data collection. Data is very valuable.
This is useful for countries where the Steam Deck is unavailable but other handhelds aren’t. Here in Australia, Steam Decks are only available as grey imports, and that makes warranty issues a potential headache, but you can walk into most electronic retailers and buy a ROG Ally off the shelf.
That said, I personally wouldn’t buy a handheld that didn’t have touchpads, so I bought a grey import and have had no issues.