They were letting them smuggle weapons into Gaza. In exchange for Hamas and the Muslim Brotherhood(two peas in a pod) to not do any naughty things in Egypt.
Basically the Egyptian government was letting the Muslim Brotherhood arm Hamas as long as they did not do bad things in Egypt.
Sounds similar to what the FBI did with the Fast and Furious selling weapons that were only supposed to be used in Ol Mexico.
Also, all sorts of bribery going on. A real money-maker for the Egyptian army.
There was a reason why Egypt was so miffed when the IDF took over that area. Afraid of what Israel would find. And why Egypt is now supporting South Africa’s suit against Israel at the ICC. Egypt really bent out of shape.