I think this set of royalties implies that Big Pharma assumes more than one fully replaceable - or that Momenta's drugs are NOT allowed to be fully substitutible and thus have full competition. And Momenta couldn't convince them otherwise.
Unless the explanation is that the technology, resolution and analyses methods that MNTA mastered early on are slowly becoming commoditized through the advances made by equipment manufacturers and software programmers. Not so much yet that other companies will unhesitatingly develop the processes themselves, but enough to give MNTA pause regarding the amount of rent they feel they can extract from those seeking the service.