Thorium is something that is literally a waste product that falls out of refining of rare metals. And natural Uranium is also available in waste quantities. Without even trying we would have enough for the whole world.

And then compare to that the very complex and expensive process of process of breeding tritium.

How does that make any sense?

Sure, fusion is about 3 order of magnitude denser, but fission is already incredibly dense. The increase density doesn't really benefit you in any practical way unless maybe if you are trying to do interstellar flight or something.