I guess the fossil fuel infrastructure is actually more expensive? (Drilling, refining, shipping of the fuel: all not needed for wind and solar.) But this infrastructure has already been built and paid for, and now someone with a lot of money wants a return on their investment over the next 25 years. Which is not going to happen in a world where we prevent the worst climate change.
(Also, investment to decarbonize things like cement are not going to happen if fossils stay cheap.)
(Also, investment to decarbonize things like cement are not going to happen if fossils stay cheap.)