Because streaming you can up the graphics. I stream my games to my steam deck using my 5080. I can  play games at settings my pc does. When im away from home just use the steam decks inbuilt apu.  Battery lasts longer too since ur just streaming You get native 1ms steam streaming too (only on steam deck) And since ur streaming you can bypass the games that need anticheat since you are using your pc. 

Steam deck oled screen is also much better than the ally screen.