If the US had continued to build nuclear powered surface ships through the end of the cold war, then it probably wouldn't be so expensive-economies of scale, plus you'd still have the infrastructure and training pipeline there.
Majoring in physics pretty much guaranteed you a NROTC scholarship, if you wanted one, back when I was in undergrad. Around a third of my cohort (and the ones graduating immediately before and after mine) were in NROTC, and every last one of them was earmarked for the nuclear program when they finished school.
I'd speculate that the Navy simply doesn't have enough personnel to put a nuclear drive-train on every cruiser, much less the entire fleet.
Edit: grammar
Edit2: Also, keep in mind that aircraft don't run on uranium. A carrier group needs tanker replenishment anyway, so switching to nuclear ship propulsion doesn't save you from needing to worry about the logistics of transporting large volumes of flammable liquid to the group.
The battle group still needs underway replenishment for food, ammunition, avgas, maintenance materials, and all the other various and sundry items required to keep ships functioning. Fuel isn't that big a deal when combined with all of these other items.
Also, nuclear reactors were replaced with gas turbines in surface ships. Nuclear is attractive versus the older oil-fired boilers. Large gas turbines changed the calculus. The steaming range of cruisers and destroyers with gas turbine power plants is excellent, hence the reason fuel is not a big deal to add to all the other stuff that needs to be provided for the battle group.