Most software is written without giving a thought to security. Because security is a source of cost. That was the case before LLMs, I don't think it will change with LLMs.
Now I wonder: given that the LLMs are steered by the companies who own them, doesn't it mean that they can somehow make security better? It cuts both ways obviously: that a company can read and generate a large part of the code in the world is a risk.
As an open source maintainer, I can most definitely tell you that the quality of the average PR is now better. The problem I am facing is more that some people tend to "flood" and misuse AI in different ways. But their AI writes better code than they do.