I think its because of the ease of startup -- its essentially a good looking by default blog (as long as you ignore the paywalls, newsletter signups, "Join Medi

I think its because of the ease of startup -- its essentially a good looking by default blog (as long as you ignore the paywalls, newsletter signups, "Join Medium" popups" etc) that is free and takes like a minute to get started with. So people join, start publishing then realize its too much work to switch so they just continue using it.