[forgotketchup]

Lack of qualified operators is real operational problem.

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.

[cobrausn]

What I was always told when I worked as a nuclear power operator in the Navy is that it's not so much that the people could not be found and trained, it was that on anything smaller than a carrier the engine room crew ended up being half the crew of the ship. The larger engine room crew size necessitated designing the entire ship around a larger ship crew, which introduces a whole lot of other logistical and practical concerns.