My main reasons:

Without a phone/app you can still do everything from the orbit controller. Which has a couple benefits:

1. when I sell my house the buyer of the home doesn't need to be tech savvy to use their sprinklers.
2. If my phone is dead I can still control my sprinklers to their full capability from the controller.
3. If the parent company goes out of business (much higher likelihood with rachio) and smart home features are not supported anymore (see Wink from the last couple weeks... and tons of other smart home company failures) then at least the controller will still work.