If an airline sells LHR slots, it's
usually in financial trouble. It may or may not be the case.
To be honest, what are the actual advantages of LGW over STN?
Train connections to London for sure. But what more?
I prefer STN to LGW. LHR is still no. 1 for me.
The Gatwick Express and most trains to London are operated by Southern.
This company has the worst ontime record in Britain. The Gatwick Express is extremely unreliable. If you want to catch a flight, this is a big factor.
LGW South is a dump in my eyes.
Compare that with LHR T2 (with the suberb lounge offering for premium and status pax)!