You couldn't post pictures on early Twitter. You had to use a third party service, twitpix. So people did. I remember Howard Stern had one of the Twitter founders on, I think it was Ev, and Howard asked him why can't I post pictures on Twitter? Why do I have to use twitpix? Ev had no answer. But Twitter eventually added native picture posting, and their user base grew. It happened gradually, it didn't happen overnight.