- The Nintendo software catalog. Sure, you can emulate on the Steam Deck, but it's a chore and far from perfect, and for most people who do it that is piracy.
- The Switch is far less bulky, and has better battery life, less noise. ARM architecture is very well-suited to mobile gaming.
- The docking mechanism is seamless and the dock is included with the device. Games are designed around that functionality specifically, e.g., you won't have controller or display configuration issues on a Switch because it's all pre-configured.
- The price is almost certainly lower.
- You can buy physical game cartridges and resell them, which is a big advantage for fans of physical media.
- The Steam Deck does rely on a lot on its compatibility software with PC games, and while it's mostly a non-issue there it's not by any means a perfect catalog. If you get a Switch, all Switch software is going to work and was made for and tested on a Switch.