There's actually two "why" questions there. First: you can tell most IPIX-aware investors (the "market") don't have much faith in B because they are not assigning much value to it. (That's the low share price. It's clear as day.) It says a deal is not likely.
Second (and this is the "why" you were really asking about): likely, because B-OM was not granted BTD for OM, which was troubling since OM is in such desperate need of therapies and BTD was granted very recently to another Phase 2 drug (Galera's GC4419). Our OM trial results had some hair on it (that's not unusual). With our IBD trial: mucosa inflammation in IBD can be episodic, so even placebo-controlled trials can be hit/miss.
B very likely has real anti-inflammatory properties, and its potential is really enticing, but you can see why BPs are not pulling triggers immediately. They're taking their time, getting comfortable with the data and results, one has apparently gotten cold feet. A deal is not a given. Management insists we've got interest, and I do not doubt that.