Because for an extremely successful company, it seems like they have no idea what they're doing.
"On Wednesday, users discovered a glitch that gave them access to supposedly private information in the accounts of their Facebook friends, like chat conversations."
This latest flap (#4080) has attracted some oversight attention:
On Monday, Sen. Chuck Schumer, D-N.Y., asked the Federal Trade Commission to examine the Palo Alto firm's latest moves to increase its social-networking presence across the Web and to issue privacy guidelines that would ensure that all social media companies protect their users' privacy.
On Tuesday, three more senators joined Schumer in a letter to Facebook Chief Executive Officer Mark Zuckerberg. Sen. Al Franken, D-Minn.; Sen. Michael Bennet, D-Colo.; and Sen. Mark Begich, D-Alaska, asked Facebook to take "swift and productive steps to alleviate the concerns of its users."
While I doubt a sternly-worded letter is going to make Facebook wake up, the sentiment behind this quote from the NY Times story might:
"Facebook has become more scary than fun," said Jeffrey P. Ament, 35, a government contractor who lives in Rockville, Md.
Mr. Ament said he was so fed up with Facebook that he deleted his account this week after three years of using the service. "Every week there seems to be a new privacy update or change, and I just can't keep up with it."