I'm sure it's more to do with making sure that students have a basic foundation of knowledge for the subject they'll be studying rather than some imperialist agenda, with more advanced classes being less and less centered on Europe. But while they're still developing the skills they'll need for these more advanced classes, it's probably just easier to keep things centered on Europe. It certainly doesn't hurt that Europe and its colonial diaspora have been very influential on the world stage over the last 500 years.