I think this is largely a business model thing - because your phone is virtually always on your person, it is a very rich source of information useful for advertising. Because of that, there are more apps that build their business model around harnessing that kind of data on your phone than on your pc. The ones on your pc that do this are mostly websites, not installed software - if your browser allowed that kind of access, you'd probably see a ton of websites abusing it in the same way as mobile apps.