Inertia. If I remember right, if you look at how the distribution of new power sources rather than existing ones, more than half of new power is renewable.

Because renewables have improved on a timescale short compared to the design lifetime of typical generating equipment. This is an unusual situation in the power business, and it means much of the installed base is zombie tech, obsolete stuff that wouldn't be used if the cost weren't sunk.

Within America, at least, there are still quite heavy subsidies to fossil fuels companies to keep them competitive and keep jobs local - their survival is partially due to some heavy market manipulation by the government.