TL;DR: Antec is going to be selling a Steam Deck competitive device, based on the Ayaneo Slide. The device has a slide up screen that reveals a keyboard, which is good because using desktop windows is much easier with a keyboard. However the device’s lowest estimated power draw at low/no load is 15w, meaning it will use comparable power to the deck running at max power. This means the battery life will probably be pretty rough when compared to the Deck. It will also likely have a much higher price point.
Why not 1080p?
Increased battery drain for diminishing returns. From the distance and screen size, it wouldn’t be that noticeable, but the performance drops would be.
As someone with a 4k OLED phone and a Steam Deck OLED, the difference pretty well screams at me. I don’t mind it so much though. It’s still pretty damn nice!
You also lose integer scaling if you need to run a game at common resolutions below 1080p. (720p/800p, etc.)
Eli5?
Is it because 1 to .75 gets weird when it’s a pixel?
Yeah - the operating system (or perhaps the display hardware itself, not sure) has to stretch each software pixel to a fractional amount of larger hardware pixels. In the case of upscaling 720p to 1080p, each 720p software pixel has to stretch to 1.33 hardware pixels. This forces blending to occur, which makes the image less sharp.
The worst part of this in my opinion is reading text.