For one, because Tinsith (who never once tested a pellet hop) stated that for pellets "All bets are off" (meaning with regard to his research and IBU's calculation formula). For another, if you look up the dissertation titled "What's Your IBU", by Michael L. Hall, Ph.D many of Tinseth's competitors have ideas here that are nowhere near a factor of 10% (or 1.1). Mosher says the factor is 1.33. Noonan says it scales from 1.0 to 1.5. Garetz had 1.1, but only from 10 to 30 minutes into the boil, else unity. But at a major hops symposium held in Germany a few years ago a guy named Christopher S. Hamilton, Ph.D, at Hillsdale College gave a pellet hops utilization presentation that put a fork into the presumptions of all of these guys. And he found that pellet hops deliver all of the IBU's they are ever going to deliver by about 40 minutes into the boil, as opposed to by about 90 minutes for the various of whole hop derivations. And he also found that within only a few minutes of boiling a pellet hop has already delivered a rather huge percentage chunk of its total potential IBU's, whereas a whole hop derivation is hardly getting started.