I would bet that border is not truly "sealed."
Also, during times of humanitarian crisis, Egypt has been known to open the border. 80 or 90 thousand Palestinians live in Egypt as refugees.
That said, Egypt had that curious double election recently, where they elected Morsi, he wiped his ass on the Constitution, wrote a new one, fired people, started ruling by decree, and got thrown out by the very guy (religious, too) that HE chose to rule his military (oh, the irony). Now that guy is running the show, after a 2nd turn at the ballot box. USA, even though they didn't care for Morsi's methods and his backward approach to things like women's rights, equality, and child marriage, affected a preference for him owing to the whole "democracy" thing, so now al-Sisi is under the gun to "play ball."
Truth is, Egypt relies on a lot of people--including USA--for foreign aid. And they need it more than ever because their tourism dollars just aren't happening. It's Ramadan (finishing up next Monday, people are tired of not eating/drinking all day--it's fun at first, the last week is the worst), it's HOT, and people get killed over there--it's just not a friendly place these days. They aren't going to make matters worse for Israel. They want Hamas to STOP doing what they are doing, for the status quo to resume, and this is one way to force their hand.