Not really sure what your point is. Apparently BA did not make any money by getting you to LCY for 150 GBP and throwing in seating, bags etc. for free. Otherwise they would still be around, raking in profits. If all the IoM can sustain is a London service by easyJet, it certainly is not easyJet's fault.
As we are just at it, British Airways served IOM-LGW for many years when there was no LHR service at all and LCY was served by the likes of VLM and Euromanx.So not really sure what the issue with LGW is. It used to be the island's "flagship" route for quite some time after it lost, like many other UK destinations, its LHR service.