"There is not a native app on Steam deck today," said Andrew Fear, GFN boss, back in January. "Use a Chromium browser to make it work. I would say that both Nvidia and Valve, I think we're both interested in making [GeForce Now on Steam Deck] better. But we don't have any announcements on a native app coming to Steam."
Yup but it enables gamers with lesser hardware to play these games.
Not everyone is as lucky to have the hardware to run things locally or streamed from their beefy PC.