It seems to me they're trying to offer a career path to a group of people who could use additional options.
If we assume that attributes that make for good programmers (design skills, intelligence, etc) are equally distributed, there are a lot of really smart people (that could become programmers) out there that have something blocking their opportunities.
Things like bias, culture, and upbringing play a huge role. Earlier this year my step-niece (age 21, working on her bachelor's degree) was told "you're far too pretty for all this school, you should just find a nice man and marry him." These exact words came out of her grandmother's mouth. That's what these kids grow up with.
I firmly believe that part of the reason my son has been so successful is that we never expected anything less from him. He knew from kindergarten onwards that college was simply the next school after high school. His decision was "where", not "if". That's far from true in a lot of families or for a lot of kids.
Part of what Gates and Zuckerberg are trying to do is get the message out to these kids. If they don't hear from someone who says "you can certainly do this", they might never try.