Over time, as the event gained in popularity, speakers shifted from developers to developer advocates.

Last time I attended (2023 edition, IIRC) one of the talks was from some Intellij dev-relations person: the talk was about the importance of unit testing or something like that, completely devoid of any value for anyone who hasn’t started coding yesterday. The speaker was obviously not a technical person and gave a strong impression they were presenting content they barely knew anything about. I seriously doubt the slides deck was put together the night before. It was an utter disappointment. That was it for me. That’s a glaring example of what the OP is talking about but other talks I had listened to were only marginally better or on par with that one. That’s when I decided the thing was so much not worth the (hefty) ticket price + cost of transportation + accommodation.

It’s a sad state of affairs but not unexpected.

This isn't exactly unique to Go. I used to attend a big Java conference once per year and some of the main speakers would be there year after year. And to be honest, I didn't think they were very good speakers in that most of what they peddled was opinion, flavor-of-the-year style talks and advice that lacked specificity and often wasn't actionable. Some of the bigger names would routinely present pseudo-research fooling gullible developers to believe in things that were not true. But the conference was well-attended.

The thing is: conferences are expensive to organize and are financially risky. You need to attract an audience. The easiest way to do this is to have a roster of well known names. If none of the speakers are familiar to most of the audience, it will be harder to sell tickets.

If you want to change this there is one thing you can do: give talks yourself or recruit someone with something interesting to say and get them to give a talk. Complaining about conferences being conferences doesn't help. You are just stating the obvious.