Why some mobile applications don't have associated desktop version?

Mobile kind of took over from desk top and mobile apps are what sells. You have to program somewhat differently for desk top versions and it’s often not worth it.

It usually takes a significant amount of additional work to make a version of software for a different type of platform.

Part of that work is the design, and mobile apps are designed for a different type of device with different way of using it, different screen, different situation of the user, different expectations of costs and features.

Sometimes it makes sense anyway, so there are parallel applications for mobile and for computers.

Computers tend to be more powerful and have much larger screens and easier text entry and more precise selection devices (keyboard and mouse on huge screen versus fingers on small screen), and expectations for what a piece of computer software can do are often greater, especially if you’re paying more for it.

Also, part of the purpose of many mobile apps is actually to fool the user into letting a company mine the user for various kinds of data, which isn’t as available on a computer.

GPS apps only make sense on a mobile unit.