And I'm not entirely sure the one where they didn't have a definite deadline for was necessarily a "made up" deadline. This is a commercial brewery, not a bunch of guys screwing around like us. They probably sell those beers in advance and make them for a specific time. So if a 60 minute IPA takes 2 weeks to make, and they need to ship out a large number in 7 weeks, by my math that gives a 5 week timeline for spitbeer to take up a fermenter. Any longer and they are interfering with their core products.
And its not like they can keep a few fermenters open for experimentation; every day a fermenter goes empty costs them lots of money, because it isn't making them any money and they are still paying for it. Likewise, a beer that takes 10 weeks to ferment out would also cost them lots of money, because they could not use that fermenter for their core products.