Israel prefers to have Palestinians warring with each other in separate factions. As long as Hamas and Fatah could not co-operate Israel was able to try to work out a deal with Abbas and the Fatah faction who were relatively weak because of the split. Hamas was simply ignored.
Hamas was left to rule over Gaza a virtual prison complete with a naval blockade and regulations that only allowed into Gaza those items that Israel wanted. At the same time few exports have been allowed making the strip a welfare client of Israel and the international community. Even so Israel feels so threatened by any unity among the Palestinians that it is willing to cut off power and water to the Gaza strip.
Israel also collects taxes for the Palestinian authority. It already froze tens of millions of those funds as a punishment for Palestine's becoming a full member of UNESCO. A senior Israeli official said that if a partnership were agreed to by Hamas and Fatah the transfer of those funds would become impossible.
No doubt little if nothing will be said about this and the press and media coverage will be light. The defense of these measures will be easy: Here is the line from the Israeli Deputy Foreign Minister. A unity government "would transform the Palestinian Authority into a terrorist authority and would put an end to any hope for a peace agreement" Of course Israel itself used terrorist tactics in gaining its independence. While Hamas has itself used terrorist tactics at present it tries to keep more radical elements in Gaza from firing rockets into Israel. For more see this article.