Any old excuse would do - the Turks are clearly bent on earning their arab street cred and that must include treating Israel as a pariah state. You can't cozy up to the Iranians and their Syrian puppets without a healthy dose of Jew-hating and paranoia infesting your every decision. In this case, however, Turkey seized on the UN report exonerating Israel for last year's unfortunate flotilla incident which left 9 terrorist-wannabes dead. And, when I say unfortunate, I mean in the sense that several Israeli commandos were seriously injured.
Anyway, as most people should know by now, the UN had no recourse but to report that the Gaza blockade is legal. Had they been able to come up with another conclusion, I've no doubt they would have. But, no, the UN admits the running of weapons into Gaza via the sea is an existing and existential threat to Israel and it questioned the motives of the flotilla's "humanitarian organizers". By extension, if the blockade is legal, running it must therefore be illegal. So, it was the flotilla that broke international law, not the Israelis. Further, it was the Turkish government that allowed this farce to occur with, I imagine, the clear intent of embarrassing Israel. They, apparently, did not realize the Israelis are serious about their security.
Luckily for the Turkish government, in the arab world, you can pass anything off as a Jewish, Israeli or Zionist conspiracy, thereby avoiding what really irks them - being humiliated. When your armies are defeated, you claim victory. When a few dozen gunmen are killed, you yell, "massacre and genocide". When your citizens revolt, you blame the Mossad, etc. Hell, last year Egypt blamed Israeli-trained sharks for a spate of biting attacks in one of its tourism areas. And, that was when the Egyptians were still being run by Mubarak, one of the least Israeli-hating of the arab thug leaders.
So, rather than make amends to Israel for essentially underwriting an attack on a country that had been mostly an ally, the Turks demanded an apology from Israel. Israel, having already publicly expressed deep regret at the loss of life (one imagines the reaction inside the halls of power was somewhat less sympathetic), refused. The Turks have decided this is cause to end a diplomatic and business relationship that has been one of the few anywhere in the Middle East built on mutual accommodation. It is Recep Tayyip Erdogan's plan to continue Turkey's move to an islamic state and it goes hand in hand with purging the army of its secular leaders and becoming ever-more chummy with Iran.
Israel, being Israel, will likely take this slight and put on its normal face of regretting the Turkish actions, calling for reconciliation and refusing to issue any other public apologies, hoping all the while the Turks eventually come to their senses. Sadly, I have my doubts. If I were Israel, I'd be very tempted to take two diplomatic steps of my own: 1) publicly recognize the Armenian genocide and 2) call for an independent Kurdish homeland. Sometimes, when you're in the sandbox, you have to toss a handful back at your tormenter.