I said academic community is a big thing because it was the students and academic staff who gave the impetus to facebook to be where it is today. They have the numbers and hence the power to do so if the product appeals to them. Here is an interesting article on it: https://www.theatlantic.com/technology/archive/2019/02/and-then-there-was-thefacebookcom/582004/.
Yeah, my first facebook account was when I was a graduate student, probably in 2005, I guess. They were slick with their guerrilla marketing, too. When I signed up, I actually thought it was something that was sponsored by the school.
I've been thinking for a while that Steem needs to stop trying to onboard everyone everywhere and focus, instead, on bringing in groups of people who share common interests, one group at a time. It's a lonely experience to get here by yourself and find yourself surrounded, entirely, by strangers. As that article & facebook's history demonstrate, colleges and universities seem like a natural fit for the group-onboarding strategy. Local geographic communities are another possible niche, but that's a topic for a diferent day.