Mobile games have to be playable on a touchscreen. There are junky cash-grab games on every platform, the Industry guarantees that. But mobile has the added challenge of a totally new controller. I think that because the touchscreen is so different from anything before, the games often struggle to have really good controls.
Most ports from PC or console rely on the on-screen buttons and joysticks, which is not ideal. Have you ever enjoyed trying to use the on-screen keyboard with your console controller? Its clunky and inefficient, like using the wrong tool for a job and taking twice as long because of it.
On the other hand, games that are specifically made for touch control may be innovative and can really shine. But they are now totally in uncharted territory, with very few or no previous titles to learn from.
Basically the "meta" of mobile controls is just starting to form. To echo Aloofdev's point, PC games were all over the place with their controls for some time. WASD was not a standard thing, so it was just straight up wild west as far as what you were gonna get for default controls. The thing is, keyboard and mouse offers the most buttons, and assuming your game allows full configuration, players will find the best controls for you (where do you think WASD came from?). Quite a few console titles have suffered from not letting the player remap the buttons freely. I think mobile will suffer even more... it will take longer to figure out what works because most games won't allow any reconfiguration at all. For a lot of games, it's not even possible to offer that. How could the player change the control in Fruit Ninja?
If you're an adventurous developer though, it's a great opportunity to create something totally unique. Touch control is limited in some ways, but it can also do things that keyboards and controllers can't. Capitalize on that!