I too thought this was odd - why just the two Miami flights?
Arriving off the early morning one recently - had to treck all the way across to T4 to use the arrivals lounge. They should at least provide an airside bus for those who wish to use it - I had to catch the underground!
I'll be annoyed if someone tells me it's because of lack of gates at T4, as we had to wait
30 minutes for our gate at T3 to become free and this was at
5:40am 