BA would need crew as well; BA haven't got enough crew as it is, and wet-leasing to sit on the slots in the mean time is going to be nigh-on impossible until the 737 MAX farrago is sorted out. All wet lessors are beyond fully booked at present.

But then BA never saw a slot they didn't like and if BA doesn't buy them a competitor will - so BA might well feel they have to buy the slots and sort out aircraft, crews, and routes to operate later.

This would all be a lot easier for BA to arrange if they weren't royally pissing off their flight crews at the moment, but that's a different thread