The problem isn't as much Spirit, but the small International terminal in FLL. Besides Spirit, which is the largest tenant at T-4, all of the international carriers use T4 for both arrivals and departures (less BahamasAir) and US and AA use it for international arrivals., and some of the Canadian ones are bringing in multiple A330 and 767 aircraft on the weekends. The airport, and T-4 were not built for the kind of traffic that is now passing through it on a daily, and especially weekend basis. This is the main reason why US pulled the majority of their international flights from FLL.