Earlier quoted context omitted.
These submarines have 95% enrichment fuel. You only need ~10kg to make a high yield weapon with the right design. You're going to get multiple weapons with the fuel stored in a single submarine. Cruise missiles are vulnerable. They can be intercepted and shot down, and they give your position away. Low reward, high risk. Nuclear deterrence can certainly be worth it.
I doubt they will use 95% uranium. [This guy]( https://theconversation.com/how-do-nuclear-powered-submarine... ) says it is about 50%. Still that is the level Iran is being sanctioned at.
Other countries use more weakly enriched uranium, the US and UK are the exception, so I understand the error in the article above.
See this better source ; https://fas.org/blogs/secrecy/2019/06/naval-reactors-leu/