70 flights a day between the two cities and British Airways increasing flights on LCY-GLA hardly suggests the route struggling for traffic
If Ryanair are struggling on Scotland - London that's a clue. There was a post by anna_lyst(sic) a while back with the actual numbers showing the collapse in recent years. On my last few trips to GLA, the old domestic pier seems like a ghost town.
When I was growing up BA was flying 14 B757s a day with BD on 8 B737s each weekday to LHR from GLA. It's now 9 BA and 6 BD, on a good day.
The coming of easyJet coupled with electrification of the West Coast mainline AND the domestic passenger duty have all hurt the numbers. Also BA are keen to move runway capacity at LHR to more lucrative long haul and punted point to point traffic to LCY. Domestically BMI have scaled back BHD, GLA, EDI and dropped MME and LBA completely. They have also closed the cabin crew base at DUB recently and scaled back frequency. AMS and BRU were dropped, AMS completely, BRU surrendered to STAR partner SN. This is a retreat from the old British Midland into new routes that LH think can be sustained. Hence the focus is moving away from the routes that Diamond Service built, onto medium haul ex BMED and flying for STAR partners like LX (LHR-GVA) and LH (poss MAN and BHX to Germany )
Take away the need to connect GLA into STAR at LHR and I think the temptation would be to leave it to the locos and BA. If they announce GLA-FRA then I think that might be a clue.