Holding the STLs until the physical models are delivered seems like a bad call to me. The original backers paid for physical terrain, in some cases painted ready for the tabletop, not for a shot at the printing hobby. This is not like traditional media such as a board game or a novel. The products are dramatically different. They could have contracted one person to prep the STLs, given them to the Kickstarter backers for free as a bonus, and made loads on the digital sales in the interim.
As it stands I think what @dreadknot69 said above is accurate and will ultimately hurt sales. When the Kickstarter launched there were not as many options for modular printable buildings. There has just been so much development in the industry in the last 2.5 years; multiple programs have been developed to allow users to create their own terrain and we are still waiting on our first shot to begin weeklong print projects.
I was definitely on board when the plan was announced to make the files available and because I am a junkie will probably still pledge here but I can understand why many folks with similar interest will hold off considering how many files they may now own, let alone how many buildings they may have already printed and have sitting on their shelves.
Just some thoughts on the business decisions. I love the work and hope to print it soon.