Why was the aesthetic standard to be pale when workers worked the fields and royals were inside, but tan when workers moved into factories and only the rich could afford to go on a beach vacation?
Aesthetic standards are formed by association. Its why sites that are "well designed" but obviously just use a squarespace or wix template feel so cheap. Why millenial flannel went from hip to standard to outdated. Why purple was the color of royalty before we could synthesize the pigment.
Having good design is about associations. Whatever design LLMs will default to, it will always feel cheap because we will learn over time that that design means cheap. Having good taste is about being ahead of the curve. An LLM cant be ahead of the curve because then that becomes the standard, and theres a new ahead.
You can use LLMs to make novel looking websites by carefully telling it to add certain details, use certain elementd, etc. At that point youve looped back to being a graphic designer.