Power generation is easy to be competitive though.

Yes and no. It is until you need to phase out coal or do a nuclear buildout. And it is still critical infrastructure.

And if you underbuild it becomes a problem for the users. And if you overbuild... well, let's assume investors won't let you do that. So, once public sector guarantees demand for decades upfront, it becomes more sensible for it to just have the plant older-built and run it itself.