nobody at Twitter really has a feel for exactly why the core product was successful
My 2 cents...
When twitter launched, Facebook was still closed to the general public, personal "blogs" were popular but somewhat out of reach of the general public (setup complexity), and a lot of people realized that while they had things to say, those things weren't enough to fill a blog.
Twitter allowed people to converse publicly, put micro-blog style opinions out, and do it without needing to register any domains or customize a page (MySpace).
IMO, twitter primarily filled a time-sensitive gap that has now mostly been overtaken by aspects of Facebook, Linkedin, etc. Much of Twitter is kind of paparazzi-like, and if a company came along that really leveraged the celebrity and sports icon base Twitter would fade away to a bunch of "SEO and Marketing Experts" all tweeting pre-scheduled thinly-veiled promos at each other.
That might have been the spark that lit the fire but I believe that people who are NOT celebrities that tweet actively, do it to reach a broader audience and engage in conversation with others in their vertical. This is in stark contrast to the network you would have in Facebook which is much more intimate.
Twitter is the internets water-cooler conversation.
Facebook is the conversation you have at home with your family and friends.
My 2 cents...
When twitter launched, Facebook was still closed to the general public, personal "blogs" were popular but somewhat out of reach of the general public (setup complexity), and a lot of people realized that while they had things to say, those things weren't enough to fill a blog.
Twitter allowed people to converse publicly, put micro-blog style opinions out, and do it without needing to register any domains or customize a page (MySpace).
IMO, twitter primarily filled a time-sensitive gap that has now mostly been overtaken by aspects of Facebook, Linkedin, etc. Much of Twitter is kind of paparazzi-like, and if a company came along that really leveraged the celebrity and sports icon base Twitter would fade away to a bunch of "SEO and Marketing Experts" all tweeting pre-scheduled thinly-veiled promos at each other.