The thing is it's a complete waste of tax payers money. Millions are spent on an airport that will generally attract low yielding pax meaning the airport makes buttons on them and thus makes a loss.
As soon as Ryanair get a deal they can't refuse at GLA they'll be out of PIK. FR are starting what could be said as PIK " bread and butter" routes this winter at GLA. They have very little hope of attracting a low-cost airline never mind any decent charter or legacy carriers.
GLA and EDI are not going to get "full" they will simply expand when needed.
It's not an opportunity waiting sadly it's a candle slowly burning out.
Maybe they could just close down the terminal and focus on training flights ,cargo and all other non passenger operations. That could be the last hope IMO