The reality might just be that most technology is slow to spread? But it also depends on what you mean by slow. The name ChatGPT became part of popular culture extremely quickly.
Also when you use Google via an alternative frontend like startpage you get a slightly better version without the crap than the one currently serving at google.com. If you use Kagi which most of the time only shows results from the google search index it becomes the best quality Google ever had.
I believe it is really only the "frontend" that is responsible for the current quality and very much an intentional choice. If Google wants to be better, it could choose so tomorrow. Actually it doesn't, because it already does today, just not on a modern browser on google.com .