Yeah MIA is very far out of the way for that route. Your basically flying the entire eastern seaboard south. That is likely not a valid connection and would be a lot of flying time.

LAS has a lot of leisure passengers and very little business traffic except for conferences which very few people nowdays can probably expense First class. That is likely the reason, AA is just trying to stimulate people to buy the F seats which is very smart. Make it an attractive price to try to win someone who wasn't even considering F.

JFK-LAS is a great route to actually book F especially if you are non-elite and were gonna pay for luggage and on board drinks anyway.