The hip hop culture and basketball have become synonymous with each other. Thanks in large part to Allen Iverson but also due to both being very popular with young black males and minorities in general. The two most common forms of "success" that young black men see black men achieving is in sport or hip hop (which is a whole other political issue I'm not going to get into but let's just say the NBA could do with a having a few more owners and front office personnel who aren't rich and white)
Plenty of rappers have wanted to be ballers (celeb ASG proves that) and they often have metaphors and lines about basketball in their records.
Plenty of ballers have wanted to be rappers and even went as far as releasing albums.
The two are completely intertwined now. Anyone who is oblivious to that isn't following the culture.
It makes sense that a basketball video game would have a soundtrack that caters mostly to hip hop heads as there is a massive amount of crossover between the two. It wouldn't hurt to have other songs on there but the people who this is aimed at are the same people who buy it to get the USA national team, the casual fan. The ones who 2k is targeting because they outnumber the hardcore fan 1000 to 1. At the very least.
They know their market. They aren't stupid. They know fine well that this is what sells. And this is the kind of thing the casual fans care about where for the rest of us it's just a throwaway topic, a passing thought. Nothing of note.
For me it's not a case of "should it be hip hop" it absolutely should, like it or not basketball is now integrated within the hip hop culture. The real question for me is "could they find better examples of rap?" But honestly we all know it's about what sells not what's best.
But hey, that's just my perspective.