[en.wikipedia.org...]
why is everyone on Facebook and Twitter using Bit.LY has the URL shortener
Because they're she.ep...lol:-)
Bit.ly: The link shortening startup is still the kingpin in its space for now. It handles about 58 percent of shortened links that pass through Twitter, according to eminent retweet button maker Tweetmeme. But that’s down from above 80 percent earlier this fall as Google and Facebook launched their own link shorteners and custom-made ones took hold. Some of those custom-made shortened links might be Bit.ly-produced, though, since the company launched a professional service for publishers like The New York Times. ...etc
[digital.venturebeat.com...] that kinda answers part of my question...
[en.wikipedia.org...]