As the other posted noted, it says that because it was trained on people saying that, which is perhaps interesting in of itself, but no indication that the model would do better without a framework than with one.

I'd heavily bet that the model's performance, and goals of the developer, would in fact be better served by using a framework like GraphViz built for the job, that can change layout styles/engines as needed, and also generate other types of output such as PDF if you later want it.

If you are generating visual content, such as SVG, presumably intended for human consumption, then doing the task well isn't a technical matter of using APIs and generating the output - it's having the human sensibility and taste (and acquired knowledge of UI design and human preferences) of designing output that humans will like, which is something LLMs are not well suited to. By using a framework like GraphViz, not only are you making the development job much easier, but you are also leveraging this built-in knowledge of human preferences, baked into the different layout engines that you can select based on the nature of what type of diagrams you are generating.

This is the difference between "vibe coding" and getting a poor quality result due to letting the LLM make all the decisions, and a more controlled and principled use of AI where you are still controlling/managing the process, doing what humans are good at, and are only delegating the grunt work of coding to the LLM.