The Pro is a great option. The adjustable grip was well thought out, everything is ambi if I remember correctly. The forend is relatively tall. It's another choice - not better or worse, but just another slightly different option.
Total guess, but it seems like everyone was turned-off when MagPul's price was competitive with similar chassis. After the Hunter came out for +/-$250, it seems like everyone was expecting the Pro to be a +/-$500 option - again, totally guessing.
I know LA Police Gear closed-out a bunch last year for really cheap (~$600 range)....unfortunately they will forever be that price in my mind, haha.