To directly address your question, I would venture the major obstruction to universities developing their own textbooks is the publishing industry lobbying. You can read more about this in Educause Review. They state the major roadblocks are: discoverability, quality control, bridging the last mile, and acquisition. But here is an alternative that some universities are piloting to help with those.
Developed by Michigan State University, LON-CAPA or Learning Online Network with Computer-Assisted Personalized Approach is a course management and assessment much like Blackboard and WebAssign systems. The system is open-sourced under GPL, so has no direct licensing fees to use. At my institution, such a system is used to avoid the massive fees on the students that WebAssign currently uses as support. I just want to mention, that as a content manager, it is not meant as a complete replacement of Blackboard systems. In fact, it can work in sync with Blackboard, synchronizing grades between the systems. Here is an flyer about the LON-CAPA system.
For the content on such a system, it seems that some publishers do provide resources for the LON-CAPA system, but in more of a bulk pricing instead of price per student. A resource that I found is Course Weaver. Their pricing system seems much more reasonable than the large fees with ones like WebAssign.
There are other resources for free open source textbook as well. Check out College Open Textbooks. One feature of LON-CAPA is a cross-institutional repository of content for courses, so if you pick a textbook, you can use problems from other similar courses. You can check out the Step-by-Step guide for an idea for how it works.
Additionally, it seems that there is some research into the effectiveness of such a system: Experiences using the open-source learning content management and assessment system LON-CAPA in introductory physics courses - ResearchGate. [accessed Mar 20, 2015].
I must say, this is just what I've looked into. I have not interacted with this system, so I don't have any personal perspective on it. It seems I could be using it as early as this summer or fall, I can update then with a perspective if I use it. I'm also not in a position to comment on the future course content that we use just yet.
Another additional alternative is the Open Courseware from MIT. I have not looked too much into what they provide, but it seems comparable.