The operative phrase being "a site you control." On Twitter, for example, one doesn't really need to think about community building. The built-in follow, mention, and other features of the platform are designed to perform that function, and they do it fairly well in the sense of fostering cliques, echo chambers, and parasocial relationships between influencers and their fans. A personal website doesn't come with a ready-made audience. You have to do a lot of leg work to even get noticed. That said, my two-month-old personal site is getting more eyeballs than my last Twitter account ever got. Rolling your own can be much more rewarding than opening a social media account over the long haul.