What works about the switch is the option. I can play handheld or pop it in its dock and play on the TV with other people. Phones never quite got this. They had the mobile part built-in, but attempts at multiplayer on a screen were either ignored or botched horrifically.
There's another big challenge with phone games, in my opinion ...
Phones are also very personal, and I've observed that people are less likely to commit to longer-term games on their phones for some reason. Some of it is no doubt inertia - the early games on mobile were meant to be played in full in under an hour. But part of it is - I think - that having your phone occupied by something persistent like a game robs people of their ability to use the phone in the open gaps we normally use phones.
Things like Switch or Stadia or whatever are dedicated gaming devices, even if they slingshot from your phone's computing power. I can use them and still have my phone in front of me. They do one thing and get out of the way.
That's all depressing to write out, but it's the world we live in.