Furthermore, many Bristol area business people have become used to using LHR over the years;
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My son, when working for a major US company, was routinely booked from LHR for US travel until I asked him why he didn't use the CO route to EWR from BRS. He wasn't aware of it and his company's booking agents either weren't or, if they were, ignored it.
These are really good examples as to why it takes so long to establish a new route. Changing habitual behaviour, and educating people to new opportunities, takes years. Even now I find that many people in the West simply don't even think of BRS being a viable option for long-haul, and are incredulous that you could fly to EWR direct on a schedule airline. I would put that down to stellar route growth which outstrips peoples' ability to update their perceptions of BRS as an airport. That, I suspect, is compounded by Easyjet being the most prominently marketed airline at the airport, supporting the idea that BRS is a LCC airport, and not somewhere to start a business or long-haul trip from.
These problems are surmountable, but only with a prolonged commitment. Interestingly, I can't think of another UK airport with the same mix of traffic as BRS. Think LHR (Business), LGW (Leisure), STN (LCC), MAN (no LCC), BHX (little LCC), EDI (no LCC). It will take work to get people to understand BRS = Business + Leisure + LCC.
If you're already a committed KL/AF flyer ex-BRS, you probably have FB status, which adds inertia to changing to *A. More time needed to change people over.
If LH had been able to hang in for 3 years, I think they would have a winner on their hands. I can't believe that BRS can't sustain a gateway route into the world's largest airline alliance, particularly as it seems unlikely that OW would ever be a credible option from BRS (BRS-MAD??? BRS-LHR??? BRS-JFK??? BRS-HEL???)