I guess I don't understand how nuclear power can run a submarine but can't be harnessed to provide power on land. Nuclear power seems to work pretty well in ships. It seems as if we're not framing the problem correctly.
Submarine, aircraft, and icebreaker reactors usually operate on military-grade fission materials. You don't want those to be exported all over the world. And a bigger reason is that they simply can not compete with bigger plants. 1 GW class nuclear reactors generate much cheaper electricity even after factoring in their huge CAPEX. There is one example of using a small nuclear ship-scale reactor for civilian power generation in Russia [0], but I would say it's a very edge scenario, not applicable to the most of the world.
Money is no object when making a military submarine that doesn’t have to surface to resupply batteries with diesel generators. Makes for a hard comparison to at-scale public utility construction.
[0]: https://en.wikipedia.org/wiki/Russian_floating_nuclear_power...