Interesting summary, by Benedetta Berti and Zack Gold, of the quandary Hamas finds itself in with regards to the Islamic State's supporters in Gaza and Sinai:

In sum, the Hamas government in the Gaza Strip is actively involved in keeping the broader Salafi-jihadi camp from stirring up internal trouble or goading Israeli action against the strip, which includes preventing strong ties between Gaza- and Sinai-based jihadis. Likewise, to end its isolation, Hamas’s political leaders also hope to reverse a deterioration of relations with Egypt, even though the group’s military leaders are deepening their relations with some figures within the very same Salafi-jihadi camp that is fighting Egypt—and which Hamas is fighting in Gaza. This is because the ongoing economic restrictions and aggressive campaign against the tunnel economy have given Hamas’s military wing a powerful incentive to deal with any group—jihadi, criminal, or both—that could provide the weapons and financial resources it needs. In this sense, the Hamas–IS relationship is primarily driven by economic transactions. Such ties, however, also result in ad hoc cooperation, and according to Egyptian and Israeli intelligence sources, the Qassam Brigades are selling or providing weapons and offering training to IS-linked fighters with the goal of clearing its “lifeline” passage. 

So much of the mess in Sinai (and of course Gaza) is due to this disastrous blockade.

Ramy Khoury argues in the Daily Star that the extremist movement is the nearly inevitable result of the region's (often foreign-backed) authoritarianism. 

But the single biggest driver of the kind of criminal Islamist extremism we see in this phenomenon is the predicament of several hundred million individual Arab men and women who find – generation after generation – that in their own societies they are unable to achieve their full humanity or potential, or exercise their full powers of thought and creativity; or, in many cases, obtain basic life needs for their families.

The expressions of bewilderment we hear today from many Arab and Western politicians or media analysts about why the Islamic State rose and what to do about it have zero credibility or sympathy in my book. Some of the same people who pontificate about the Islamic State threat were often directly involved in actions that helped to bring it about (corrupt Arab security states, the invasion of Iraq, and total support for Israel).

Peter Harling, in Le Monde Diplomatique, looks to Sunni resentment and the "void" of good governance and international diplomacy. 

At root, IS simply fills a void. It occupies northeast Syria because the Syrian regime has by and large abandoned it, and the opposition that might have replaced it has failed to secure a genuine sponsor, in particular the US. And, in Iraq, IS has surged into cities such as Fallujah and Mosul because the central power in Baghdad has largely neglected them: the Iraqi state maintained a presence there that was simultaneously corrupt, repressive and flimsy. IS’s rapid expansion into zones in northern Iraq controlled by Kurdish forces, but inhabited by Christian and Yezidi minorities, is unsurprising, given the lack of real interest shown in the victims by their ostensible protectors, the Kurds, who were quick to withdraw to their own territory.

IS also fills a void on a more abstract level. Simply put, the Sunni world has trouble coming to terms with its past and imagining its future. A fragmented 20th-century history, following a long period of Ottoman occupation which was seen as a period of decline, ended with a succession of failures: anti-imperialism, pan-Arabism, nationalist movements, socialism, various forms of Islamism, capitalism — all led only to bitter or ambiguous experiences. Thus far, with the exception of Tunisia, the hopes born of the 2011 uprisings have turned to ashes. So where can Sunnis turn to find inspiration, self-confidence and pride? The reactionaries in the Gulf and Egypt? The Muslim Brothers, who are on the ropes? Palestinian Hamas, locked in a perpetual impasse in its resistance to Israel?