A "pocketable" gaming console in the modern world is essentially a smartphone with analog sticks.

There are "controller grips" or "controller mounts" for phones readily available and you can even pair it with Steam in-house streaming or Moonlight to play games at a quality that is impossible at this form factor for cheap.

Even at larger sizes it's difficult - The Nintendo Switch only worked because of great franchises and IP. The Steam Deck also required great technological investment into Linux and platform familiarity.

It's not hard to see why barely anyone's trying...