If this is because what was thought to be in the bag no longer is
That would be my guess. Looking at the potential "full service airlines", it's very unlikely to be AF/KL and equally unlikely to be B "we've forgotten what the B stands for " A, which leaves Star affiliates like SN, BD, LH. Given that whatever strategy LH had for BD seems to be in a bad place at the moment, I would assume that they're not in a position to commit to anything.
I have some sympathy for Bristol Airport. There are some yawning holes on the European short-haul coverage, and they have tried to keep the opportunities for "full service" airlines open, but ultimately if those airlines don't see the opportunity, then I should imagine EZY would be interested in serving those routes, given their BRS base. That would probably close off the "full service" opportunity.