There are tons of reasons.
The rights are probably relatively cheap compared to UEFA or CONMEBOL but they probably rate the market as being much smaller as well. Also do they bring the Asian Cup? We questioning CAN but the CAN is only now getting attention from general football fans because of the number of players that now star in Europe and that is a recent thing.
I actually heard someone on FSC say that it's expensivie to carry. Maybe not the rights, but the overall package- I don't know nearly enough to comment.
I wouldn't bet against socio-economic & political factors at play that have an influence.....
All else being equal, I imagine if it made pure economic sense, it'd be covered on mainstream football TV.