According to Tom Simon
Years ago I thought that chip design companies would embrace the latest technology and be eager to adopt new tools. What I learned was that the people implementing and managing design projects were taking a lot of risks with almost every aspect of their projects. What they most wanted is to minimize risk from the design process – especially from design tool changes.
The reluctance to change goes much deeper. In the middle of a project a design team would never be willing to change tools, or even tool versions. Even minor updates from vendors can have subtle algorithmic changes that affect results. Beyond the obvious possibility of an outright bug, there can be variations in results that can affect every downstream step. This is true for implementation and sign off tools.
Chip companies spend significant resources on correlation and validation of tools. In some cases, known bugs in software are compensated for and if a tool vendor were to suddenly fixed the bug it could break the flow. Pretty much the only reason a design team will change any tool or tool version is to fix a show-stopper issue.