Its not the low time pilots , but possibly the very experienced returning expats that are keeping salaries low. DEC at J2, EZ, NLH is popular for the cashed up 50 somethings Ex. EK & QR brigade. Or occasionally, from Asia.
If you have a 1 million quid house paid for, kids left Uni and a place on the Costa, then its just pocket money from your work. Pilot shortage? No 'ere in the UK, look east sir.