Except if they did enable Fortnite on Deck… As the game is not on steam, people who want to play it would be encouraged to install the epic store on their Decks (which IS possible, and already something people do to play other games from the Epic store on Deck), which would give Epic an in on SteamDeck.
Enabling EACs proton support for Fortnite would be a means to get their foot in the door with Deck players, but you’re saying they wont do it because they don’t have a foot in with Deck players?