That supposes that LLMs can write secure software. Also, if we assume that finding bugs is easier that not creating them (reasonable I would say), the supply of bugs will never be exhausted.
Especially if you use AI, let's say you have it implement a feature and then change your mind. In my experience AI makes as many if not more bugs than a human.
I think we're at the point that the best LLMs can indeed write software that's far more secure than your average programmer. Partly because the average is so terrible.