Taking the period from 1968 to 2008 (40 years) Cambrian BA managed 10 years until BA were more than happy to route swap with British Misland as they couldn't make the route pay.
BM and its offspring managed 14 years.and gave up due to lack of profit and used the slots which they had for something more profitable. Since then no-one has had a serious go although any operator who had LHR slots would use some of those slots if the routes were worth it.
easyJet, with plenty of slots at Luton couldn't make that route pay.
Recently,of course, VLM had slots at LCY and used them for a LPL service. What happened? - it lost money whilst the MAN service continues and offers 6 round trips a day four days a week, 7 trips one day a week, 1 on a Saturday and 2 on a Sunday IN ADDITION TO the regular BA and bmi services to LHR and LGW
So, the figures you supplied show that in the last 40 years one airline and its successor manged to serve the route for 25% of the time, another for 35% of the time- not exactly a sustained service in the accepted meaning of the term and a total shambles from 1992. Why? Because a solid, regular and sustained demand doesn't exist.
BTW the expression " a year or three" was a throw away line to indicate the relatively shortlived periods of London service at LPL compared to the 62 years of continuous service at MAN.
[As for the figures of course context matters. Manchester losing over 100,000 pax a month is as significant a blow to its business plan as Blackpool losing 10,000.
I know which CEO I'd prefer to be.
In the context of Blackpool the figures are disastrous. In the context of Manchester the trend is unwelcome but the airport and its group, whilst recording reduced turnover and probably profit is in excellent shape to survive. If you think that a reduction of over 16% is as significant as a reduction of over 60% (in any context) you have a strange understanding of figures.
For LBA the figures will get worse when the bmi Heathrow service withdrawal shows up.