One rumor is now suggesting that authorities had to strike because of possible pressure from the music industry as the service was about to launch a music service called MegaBox that could have enabled artists to give away their music for free and get paid by MegaUpload via secondary revenue that may have been generated by tools such as advertising. Given the size of MegaUpload, at the time of its shutdown the 13th largest website, hosted on more than a thousand servers and more than 1 billion visitors every month, MegaUpload could have been a serious threat in such a venture for the music industry. Keep in mind, this is a rumor, not a confirmed fact.
Even though, the speculation that the music industry was able to convince the FBI to shut down MegaUpload just in time before there may have been an inconvenient iTunes competitor is a spicy exercise. Imagine a service that attracts 50 million users a day and gives away music free of charge, while keeping artists happy. Suddenly you don't need music publishers anymore. Has there been a shady operation in the background? We don't know and I will leave that up to you to decide.
Of course, as it stands, MegaUpload and its sparkling and money-flaunting founder Kim Dotcom (born Kim Schmitz) are accused of mass piracy and there is a good chance that Dotcom won't get away with a slap on his hands as he did when he was convicted of insider trading and embezzlement in 2002 and 2003. Dotcom received a probationary sentence in both cases.