Corporate controlled most desktops. The web allowed you to access and run stuff even when IT told you not to. Installing a program simply did not happen without an act of God.

Individuals control most phones. The goal of the developers is to intrude on your device and you have permission to allow it.

The issues here are same as "web toolbars". Developers want to intrude on your mindspace and the web doesn't allow that easily. Consequently, they have no incentive to build good web apps.