The sanctioning bodies have rankings and the champ has to defend vs someone in the top 10 or 15.
The issue with no names getting title shots comes up because usually one sanctioning body won't rank other sanctioning bodies champions, or challengers in their rankings. So they have to fill in with other guys who aren't actually the top 10-15 best at their weight. The rankings are made up by committes of a handfull of people that come from different countries and guys will be more likely to vote for fighters that come from their country.
If you've got time there's a series of great articles done by badlefthook.com about all the santioning bodies and the politics involved.
Business of Boxing - Bad Left Hook - For Boxing Fans