Because hardware becomes cheaper and cheaper, and newer/faster interfaces exist. Look at new features in smartphones past years.

Nokia orders to make X devices and they must sell as quickly as possible before their value decreases. So they add new versions and features and compete on price & features.

We also want some kind of compatibility. Thats why many people run a GUI browser such as Mozilla Firefox instead of the latest Lynx. Yet, on the NIT, MicroB eats resources for breakfast. As does Fennec. So yes, we could use more resources.

Interfaces need to be designed with touchscreen in mind, and performance as well. But if the option is either no compatibility or some slow, half-baked desktop port what would you pick? In the end, a better program wins the market share.