I think that ultimately the issue is a matrix of problems, largely the sudden economic downturn causing an artificial low in living expenses to jump to an artificial high, combined with a renewed crackdown in the wake of the earlier revolutions. Both of these have a combination of causes. The butterfly effect goes both ways; even the smallest cause can have numerous effects, and everything that happens is caused by a geometrically large history.
However, the most significant causes of Egypt's strife are the current situation and the nation's recent history. Egypt's leadership has been just as bad for the last thirty years. Perhaps the first decade was better if only from novelty, but there has been very little change in how bad the country has been for some time. This is ultimately the fault of the US, because it has propped up M. since he first came into power. Perhaps we asked him to be more humanitarian, yes, and it is very difficult to determine exactly what would have happened had he not had US backing. It is possible that he would have ruled for fifteen far worse years, or perhaps he would have been overthrown by a worse leader. Ultimately, however, Egypt would have stood or fallen on it's own, for better or worse for her people.
The more recent troubles that pushed the country over the edge are fundamentally economic and are largely the fault of the US. While the small time fraudsters may be centered in the heart of Africa, the big time thieves live in the US, and have friends in the government. It is a result of (and here you discover that my spell check only works in English) lazise-faire bank regulations that allowed the economic system to get into the state it did, and when it imploded, as it obviously would, the shock waves caused a great deal of the economic damage we see today.
Of course, there comes the hovering specter of climate change which may indeed be related to decreasing water supplies. I won't go into detail in this, but I would like to say that the US is now thankfully not the most significant contributor to this; we are now second to China.
Looking back over this, I'd like to remind any Egyptian readers that support for Dictators, loose banking regulation, and generous pollution controls are all Republican issues, and I am a Liberal. Just putting that out there. I say that and not "Democrat" because they are more centrist than I am, assuming "centrist" means "is carrying Israel's love child".