Like others have noted, I think it's far from obvious that Google's LLM prompt is the best experience in the space, I would say it's clearly not in the top tier and even that relatively speaking, I consider it bad compared to the best options.

Assuming we're talking about the AI generated blurbs at the top of search results, there are loads of problems. For one they frequently don't load at all. For another search is an awkward place for them to be. I interact with search differently than with a chat interface where you're embedding a query in a kind of conversational context such that both your query and the answer are rich in contextual meaning. With search I'm typically more fact finding and in a fight against Google's page rank optimizations to try and break through to get my information I need. In a search context AI prompts don't benefit from context rich prompts and aren't able to give context-rich answers and kind of give generic background that isn't necessarily what I asked for. To really benefit from the search prompts I would have to be using the search bar in a prompt way, which would likely degrade the search results. And generally this hybrid interaction is not very natural or easy to optimize, and we all know nobody is asking for it, it's just bolted on to neutralize the temptation to leave search behind in favor of an LLM chat.

And though less important, material design as applied to Google web sites in the browser is not good design, it's ugly and the wrong way to have a prompt interaction. This is also the case for Gemini from a web browser. Meanwhile GPT and Claude are a bit more comfortable with information density and are better visual and interactive experiences because of it.