Parents like that it's widespread because they can find old friends, but the site becomes less trendy when High School and College student's parents are using it. They need to pick either being widespread or being exclusive, but they can't be both.
"They can't be both" doesn't really mean anything. They are both. Their user base is still growing, and almost none of the people who vowed to "leave facebook" have actually done it. Some have, but very, very, very few.
As the other commenter said, they aren't both. They've chosen to be more widespread. This means that their user base is still growing, but from what I've heard it's mainly older people. I'm starting to hear from other High School students that they aren't interested in Facebook anymore, which was surprising but I can see why now.
