Twitter is great for real-time information.
You follow interesting people. You look at a real-time feed. Etc.
People use it for news and to follow famous people
The majority of users never tweet. Instead they use it follow cool people.
Twitter wanted to be the place for real time
Real time is the best place for news and information. Following makes it possible to get info from anybody and not just your friends.
But Facebook stepped in.
By adding in hashtags for indexing, promoting curated top news on the side bar, and allowing following/lists on Facebook
For mass consumers, the value prop is better on FB
Easy access to news. Killer curation algorithm. No pressure about who to follow. Follow people who come to mind. Searching gets you the public real-time info you want
So if I'm a normal user of Facebook
Why would I use Twitter?