The difference between project management vs. governance is that project management deals with delivering the short term promised result while governance is creating the environment that will maximize the overall chance of success.
They both deal with the how to get things done but the differences are subtle when looking at them for the first time.
A CGEIT is much more involved with long term business concerns than the project manager. The project manager expects the business and political questions to have been dealt with by the time they get their project chartered.
A project manager is primarily concerned with keeping a project on track. The governance professional, be it on the board or an executive or a consultant is concerned with the value delivery of the project. A project may be on track and in fact may even be making money but if it is not strategically aligned or is not delivering as much value as other projects, it may be terminated.
Value delivery is more about the long term life cycle of the project and the project manager, after having the project “chartered”, does not concern him or herself with that question anymore.
The criteria used are different. The perspective is different. And a CGEIT looks at things from a more overall view point than that of the project manager.
I am still not clear about career opportunities. There are claims about PMP average yearly salaries but I have not seen any claims about CGEITs.