One of the funniest stories I heard was about the first copy of the Intel 14nm design rules Altera got from Intel. They were heavily redacted, which is something I had never seen in the foundry business.
https://semiwiki.com/semiconductor-manufacturers/intel/7912-...
Additionally, a contract fab tries to be flexible, easier to design for. They make their libraries & design rules work well with commercial design software. A private fab on the other hand can boost yield & performance by pushing increasingly complex design rules on the design team, and the design team can use customized or internally developed software to make it all work.
So in short, they had the best fab tech in the business but they weren't used to servicing anyone other than themselves.