When it comes to community-building and social networking, the popularity metric is absolutely an important consideration. If you are choosing where to start the official community for your software project, and you choose an obscure service, people will make unofficial communities in the more popular services, and you end up with all the supposed drawbacks anyway. Normal non-technical users who are looking to join a community won't prefer an official community on a service they've never used before to an unofficial community on a popular service. That's why people make unofficial user subreddits and community Discord servers. Those unofficial communities could and in many cases will outgrow the official community. This has happened many times before and will happen many times again. Then, new users, even if they see both, will see an unofficial community on, say, Reddit with many more users than the official one, and when this happens, developers either start participating in the unofficial community posting announcements and whatnot there, and if that happens, there becomes little reason to join the official community.