Bio tech and start up style ... failing fast seems like an incompatible thing.

Bio tech seems like it often requires tons of iterations on an idea that take a very long time. Meanwhile start up land is often "nope that first shot didn't get any uptake, guess we're done".

Also BMS recently pulled out of their collaboration with Arsenal so in this case they were probably counting on more easy $$ from that partnership after burning through their previous $325m raise.