Making users go to repositories other than Extras is inconvenient, in that it requires them to hunt down a repository for each new package they install; unsafe, as Extras maintains a certain level of quality through certain QA processes and by having lots of eyes on it that random 3rd party repositories don't have; and generally acclimates users to a mindset that they shouldn't have to have ("I need a new repository for every new application" and "It's OK to add random untested and untried repositories to my tablet"), and is, thus, user-hostile.