Those things are popular? I don't even see who would want that. Just play on your iPad or phone.
Some don't like touch controls.
Some don't want to clip and unclip their phone to their pad.
Some would just want a dedicated device with buttons, say, if the TV's busy so they can still game, or to pass the kids the somewhat more durable android tablet for remote gaming than phone+pad. pad.
They're not looking to override their phone, and all the headaches that go with that experience.
There's a skism. In my mind it's:
1 - Touchscreen gaming.
2 - Portable with buttons access to your already existing games library away from main home console.
The market/scenarios certainly exist, but people don't want gimped half products. A Vita without back buttons, and games blacklisted against "casting" to TV. A PSVitaTV set-top box salvage product with no Netflix app in UK, at a time when such a thing was more of a selling point.
More recently, the 1-2 punch of a button-less phone shell/cooling fan followed by a Remote Play only controller.
Sony are the only ones with the depth and range of back catalogue of games, not to mention my stranded PS3 digital purchases that haven't migrated over to new PS+ service, like there are PSNow games which didn't transfer over. Sony are the only gaming brand I would want to bare publicly (at least if it was a new handheld form factor and not an inelegant "controller-screen").
And they just keep fucking it up, literally coasting by on PS3 era turnaround, PS4 era success and continued XB fuckups of XB's own all throughout.