Originally Posted by JulesWinfield

​​​​​​Found this:

Spirit is the fourth low-cost carrier to announce its launch or expansion from MIA recently, following JetBlue, Frontier Airlines and Southwest Airlines. Previously, the company considered MIA’s per-use fees for gates to be too expensive. But during the pandemic, the airport opened up more gates for what’s called preferred-use, offering a fixed fee for airlines that maintain a certain number of flights from the airport per day, And that enticed Spirit, Kirby said.