Presumably, Wizz are bargaining to get a better deal. Threats can sometimes help to focus minds. We should never taken it as a given that Wizz will always remain loyal to Luton. They could move some of them operations elsewhere and whilst unlikely it's not impossible. That said, I think it's unlikely that they'd upset a winning formula. Wizz + Luton is a great combination. They have major clout at the airport so are presumably using it to negotiate wit Swissport.