Why should they be incentivized to do anything, Valve takes care of the work, they can keep targeting good old Windows/DirectX as always.

OS/2 lesson has not yet been learnt.

Regardless if the game is using Wine or not, when the exceedingly growing Linux customerbase start complaining about bugs while running the game on their Steam Decks, the developers will notice. It doesn't matter if the game was supposed to be running on Microsoft Windows ™ with Bill Gate's blessings. If this is how a significant number of customers want to run the game, the developers should listen.

If the devs then choose to improve "Wine compatibility" or rebuild for Linux doesn't matter, as long as it's a working product on Linux.