The problem with the source country designation is it's a bit of a blunt instrument. By that I mean it doesn't go according to the minority or the situation; it goes according to the whole country. So if they only want to add countries to that where there are mass violations of human rights for significant groups of people, source country may not be the best solution here.
Suppose we were to add Uganda to that list. Aside from sexual minorities, how many other kinds of people are persecuted in Uganda? You open it up for basically anybody in the country to make a refugee application and try to prove their case. As I said, it's kind of a blunt instrument.
I would agree with it more for countries like Iraq, where there are sustained mass violations of human rights against not only one small group, but a whole bunch of religious minorities, sexual minorities, and political minorities. It makes more sense in a situation like that.