Personal Branding: Is there ever a good reason for someone to write on sites like Quora or Medium rather than on a site or blog they own?
It’s the only reason.
Your blog or website should act as a hub for your content.
Until you have a following, sites like Quora and Medium are the only places where you should be writing.
Because that’s where you can find audiences to draw them back to your website. Nobody is going to magically start showing up to your Website.