Phones are annoying, and the UI of most apps is user-hostile. Here are the equivalent steps you have to do to accomplish the same thing as this button does:

    - Wipe your hands from moisture/whatever you had on them.
    - Find your phone in your pocket.
    - Orient it.
    - Unlock it.
    - Exit whatever app you left running in the foreground.
    - Open the app drawer.
    - Find the ordering app.
    - Click through several layers of UI to get to the right product.

And only now you're in the same position as after just pressing a button. This is a significant cognitive load. When I realize I need to order something, I want to order it, not navigate through countless steps. Having to do more than two actions is too much.