Presumably the revocation is connected with the federal arrest warrant issued in 1992.
Also he's been badmouthing America vis-a-vis Islamic terrorism in recent years, which probably pushed his warrant a bit higher up on the stack.
This is but the tip of the iceberg, the most recent development in the story. I encourage you to search "Bobby Fischer" on FR for discussion of this since Friday, and a lot more can be learned by reading articles on www.chessbase.com, a website for one of the best chess database software available, but also covering recent events in chess. Also read the links within each article, but search FR first.
In short, Bobby has said some heinous things, but I'm convinced he's developed acute mental illness, maybe Asperger's syndrome, maybe paranoid schizophrenia, and these are manifestations of that. How it has played out in his life is truly tragic. He's done more for American chess than anyone, and a one point in time was a national Hero perhaps like no other, rivaling the US olympic hockey team and a Cold War champion.