Abdullah Schleifer knows Egypt very well, and he makes this point forcefully in his column at Al Arabiya: "Sisi wins, the turnout is low, and critics reign supreme."
While he's more optimistic about Sisi than I am, he rightly notes the fragility of the Brotherhood's 2012 victory, which it then treated as a solid mandate, overplaying a weak hand. While he recognizes the Brotherhood and leftist boycott was a factor in the turnout, he also notes:
But among the abstainers, far, far greater in number were two other constituencies that actually overlapped into one. A large number of prospective voters who remained pro-Sisi but were convinced that Sisi would win so overwhelmingly, that there was no need for them to spend hours standing in lines to vote. And secondly there were a large number of voters who remained pro-Sisi and anti-MB, but now lacked the passion, after the passage of more than ten months, that had inspired the earlier super enthusiasm. Add to that mix of overconfidence and complacency the unbearable heat wave that swept over Egypt for all three days of voting, but particularly on Tuesday with temperature around 40 C or higher. The voting centers remained open till 9pm but these past few nights the heat wave did not ease up until several hours later in the night. And when the government declared Tuesday a holiday for public sector employees and for the banks, it became a national holiday and few of the many who were over-confident and complacent felt compelled to leave their homes, however modest, to stand in line in the far hotter streets.His piece is a useful corrective to the conventional wisdom.