Also, it is quite likely that MIA is not permitted in the valid routing rules for the JFK-LAS fares. That means you're actually buying JFK-MIA + MIA-LAS which costs a lot more. I got a ~$950 fare booked into A and P for October 16th in the afternoon and it prices in that additive manner. Connections via ORD can book as the single fare component at the lower rate.