Unfortunately there is a catch 22 situation the West of Scotland and the wider central belt where you have two/three airports stretching each other thin in the space of 70 miles, its just totally unnecessary but we're going to have to continue to live with it.
PIK clearly has the better infrastructure with the runway, train station, doesn't suffer from the M8 like congestion however its nowhere near as centrally located unlike GLA.
The management of PIK have to be congratulated on improving the fortunes of the business. I still feel its somewhat volatile as its done very well out of world conflicts and crisis and one off special events all in a short space of time - Covid, Cop 26, seems to be doing well out of Ukraine too, but I guess its probably wishful thinking to think that the world will ever be totally at peace... They deserve credit for diversifying the business as the over reliance on commercial flying was close to killing it.
Ryanair have a decent operation there between all the maintenance ops and I'd imagine with no commercial competition they virtually have a monopoly on the place, so theres absolutely no incentive for them to move up to GLA and it suits them to base their West of Scotland operations out of there.