I believe that it's a physical plant thing. We have spent over a hundred years building hydrocarbon-based energy infrastructure. Much of that is still out there. Wind and solar have made a ton of progress in the last 15 years or so, but it's only really become substantially better financially in the last 5 or so years maybe. It's still going to take decades to actually replace most of that stuff, just as a matter of how fast we can build and install hardware.

Note also that it's a worldwide chart, so it includes developing countries that may not be so quick to jump on projects that are expensive right now even though they'll save a bunch of money in the long term. Though to be fair, some may have a leapfrog effect when it comes to building brand new infrastructure.