Well, what you are saying isn't really true, since about half of France's nukes are also nuclear submarine-launched missiles, as well as a large part of the US nukes and a sizable part of the Russian nukes (and China also has a few of those).

The other countries just don't have suitable nuclear submarines.

Also, I assume the UK have no plane-delivered warheads simply because they lack an aircraft carrier, making those quite useless.