Because the 28-year-old Facebook founder needs the money. He needs to hammer down his American programmers' salaries with more H-1B visa foreigners to keep his net worth up. For a terrifying moment last year, Zuckerberg's wealth dropped from 11-figures to only 10-figures. Remember, money is how these guys keep score. Zuckerberg had to endure the humiliation of showing up on the 2012 Forbes 400 list with a net worth of only $9.4 billion. There are a lot of people with 10-figure net worths (1,426 according to Forbes in 2012).
Fortunately, the Zuck is back over the $10 billion mark lately, so he can hold his head up when he walks down the street, but you have to feel for the poor guy.
Rubio has been promoted relentlessly by the media because he's non-threateningly cute, a boy band singer-dancer (the subliminally ethnic one) in a suit. He doesn't look cunning, so it's easy to still like him when he gets caught telling a another lie about what's in the bill. How can you expect a nice boy like Rubio to keep track of all those details? He means well. You can tell just by looking at his symmetrical features.
Personally, I kind of like Zuckerberg, but my approval is a pretty good contra-indicator. (I should have started the world's simplest marketing research company: just show me two new products or two new ads, and whichever one I prefer, you should junk it, immediately.)
I think Zuckerberg is, by the standards of software nerds, a good looking guy, but he increasingly strikes a lot of folks as a green-eyed, fair-skinned jerk. It doesn't help his image that it seems likely that, deep down, he's probably a Republican (he hosted a Chris Christie fundraiser). And a lot of people are growing sick of Facebook. Oh, and, yeah, there's an entire movie already about what a monster he is.