They have added a few limited routes/frequencies at EDI since GSMs demise and the article mentioned did say there was "no reason they wouldn't fly from GLA" but they were focussed on EDI for the moment. It then quoted Jet2 management as saying this was because there was more inbound demand to EDI, but this seemed a bit odd imo given that most of their routes from EDI are med/sun routes - I doubt any of them really carry that many inbound pax. Even if they did, I would've thought competing directly with FR would've wiped out any gains.
Irresepctive of this, GLA is still a big market with a large gap in service at the moment. Even though the charter carriers have improved service, people still want scheduled flights to the med/canaries for flexibility and FR are not everyone's cup of tea. There are significant openings in city type routes as well. There is significant demand undoubtedly to the Canaries at the very least, given GSM flew pretty much daily year-round to TFS and had very good loads (fares were not cheap either). Even if for some reason Jet2 are not interested in serving other routes from GLA, I'm surprised they've not at least got a 757 in there operating to TFS.