The shape of the minivan might have been groundbreaking in the 1980s (when moms were growing tired of the station wagon), but the design is hardly contemporary now. Even the best looking minivans appear boxy.
SUVs, on the other hand, have shown a wide range of design language over the years (consider the differences between a Honda Element, Chevrolet Tahoe and Land Rover Range Rover).
This diversity of design means that SUVs tend to fracture into different parts of the market and different designs appeal to different people. In turn, it allows for more buyers.
As the entire market (including, yes, moms) looks to interior design as a way to differentiate one vehicle from the next, SUVs present much more choice. You'll never find, say, the interior flourishes of this Land Rover in a minivan product.