Small Modular Reactors (SMRs), which could be manufactured in factories rather than in bespoke, on-site builds, are regarded as a technology that could bring down the cost of nuclear builds in future.
I suspect submarine reactors are expensive because of their unique design constraints, relatively small production runs, and the fact that they are contracted/built on military budgets rather than in competitive commercial environments.
Lets take a statement like this: "Nuclear reactor fuel can be low-enriched uranium, with a concentration of less than 20% of fissile 235 U. This low quantity, non-weapons-grade uranium makes the fuel less desirable for weapons production."
20% enrichment is far higher than what is typically used in commercial power reactors. Because of the exponential behavior of uranium enrichment, 20% is almost all the way up to weapon's-grade material. Its part of why Iran's stockpile of 20-40% material was so concerning - they could have very quickly converted that into bombs.
If you have the technology to crank out 20% U-235 in quantity, then you also have the technology to make weapons in quantity.
Here's another concerning statement, "Many SMRs are fast reactors..." Fast reactors are inherently capable of being used for mass-production of plutonium. Plutonium production from fast breeder reactors is far less expensive than uranium enrichment, and an even higher proliferation risk.
Honestly, I think that the only reason small modular reactors have some traction because they appear to require less capital investment than full-scale reactors, thus drawing VC slush money.