I used to go to a bunch of local meetups that had 5000+ members and to my surprise only about 30-40 people actually attended. Usually, a meetup is about something, for example, "How to save on taxes for small business in 2019" and usually they try to sell you something. You might learn something depending on how much you already know.
To answer your questions:
1) No solid connections were made, just a bunch of people who said, "Yeah we should meet and discuss this" which later just disappeared.
2) Rarely I learn something new that had any use, more like just learn interesting things.
3) No, but a good way to socialize and meet new people
My thought is that serious people don't have time for meetups because they are busy working
To answer your questions:
1) No solid connections were made, just a bunch of people who said, "Yeah we should meet and discuss this" which later just disappeared.
2) Rarely I learn something new that had any use, more like just learn interesting things.
3) No, but a good way to socialize and meet new people
My thought is that serious people don't have time for meetups because they are busy working