They can be, but at least some of the stuff the Steam Deck does (automated updates, cloud saves, specific tweaks to get it running on its hardware) would be hard to make quite as convenient for pirates for one reason or another.
I mentioned the pirate equivalent to cloud saves, Syncthing - it is absolutely great, not that hard to set up considering what it does, and I absolutely love it and it feels like magic most of the time. But it’s still not quite as easy and reliable as buying the game on Steam and relying on Steam’s servers for cloud saves.
(The fact that it’s hard to make pirated versions reliably update automatically also means that rapid updates are one of the best ways a dev can deter pirates, at least for as long as the game remains supported. I’ve absolutely pirated games that are in early access and then bought them, partially because I liked the game and wanted to support the devs, but mostly because I wanted to get updates immediately and automatically rather than having to wait for it to appear somewhere and then install it myself.)