Mainly due to the unbelievable stupidity of the average human. I previously worked as a security expert and you wouldn't believe the number of website owners that don't properly salt and store their users' passwords and the number of users that use a "banana69" type password which is easily crackable with a dictionary attack, of course the same user will be registered with his email and the email password will conveniently be set to "banana69" with both the Blockchain.info Identifier and Password saved in drafts.
Bitch and moan about Bitcoin not being secure enough after that will ya? Have you ever used the same password for multiple websites? Have you ever stored your private keys or private key entropy on a machine connected to the internet? I will begin seperating the sheep from the wolves and slapping you across the face with a wet fish bitches.
Bitcoin will never take off without centraliziation whereas a set number of intellectuals will look after the BTC of the stupid masses. Your inferior brains are the achilles heel of Bitcoin security wise, not SHA256, not RIPEMD-160 and not the ECDSA which the NSA may build a billion dollar computer to record all the sounds that your processor makes while generating and crack.