the problem is they are expensive to acquire and even more expensive to keep them in operation - I think the Brits pay over £1Bn a year just to keep their atomic weapons establishments ticking over
then you have to have a delivery system - that is believable - ............... look at the cost of the new SSBN's for the USN & RN....
then the threat - say Canberra threatens the Chinese - with (maybe) 8 missiles on boat somewhere N Of Darwin
One Chinese SSBN could take out Perth, Adelaide, Melbourne, Sydney, Canberra & Brisbane and have a few war heads left over
It doesn't make any sense
Spend the money arming the Indonesians and the Philippines if you must