Don't let the high-profile visit by the head of the Egyptian General Intelligence Service, Abbas Kamel, mislead you. I wrote about it previously – Egypt is responsible for almost every rocket that is launched at Israel from Gaza, whether manufactured locally in Gaza or imported from Lebanon, Syria or any other place.
To manufacture rockets in Gaza, Hamas needs to import raw materials and machinery. To import parts or entire rockets, Hamas needs a logistical route. In both cases, the logistical route passes through Egypt and Sinai. The sea is to the west, and the State of Israel is to the north and the east.
You also shouldn't believe the reports by the Defense Ministry or politicians in the Knesset that Hamas obtained the materials it needs for its rocket network by disguising them as humanitarian aid. Occasionally, these kinds of materials are captured at the border crossings controlled by Israel, but most of it is brought in via the Philadelphi route, either above it or below it.
During 11 days, Hamas launched 4,000 rockets. How many does it have in its storehouses? It appears that it has several thousand more. For this amount of rockets, you need a lot of metal, materials for creating propulsion, materials for manufacturing engines, machinery and more. Manpower needs to be sent overseas for training, and then returned to Gaza afterwards. How do you go overseas from Gaza? You guessed it, via Egypt. Again, officially via the Rafah border crossing or unofficially via the Philadelphi route.
Does Kamel know about this? Well, he's supposed to know about it. The Egyptian intelligence services are very concerned about the Islamic movement, and therefore they monitor Hamas in Gaza. People, goods, messages in the media and more. It isn't by chance that Kamel always serves as a mediator. Hamas listens to him because it is dependent on him.
The smuggling route of Hamas to Gaza passes, at least according to assessments, via the seaports somewhere in the area of the Gulf of Aden (the Middle East or Africa), via a land route to Egypt, and then via Sinai to Gaza. Kamel and the intelligence service that he is responsible for are aware, apparently, of most of this smuggling activity that passes through Egyptian territory.
One of the questions being asked is why Egypt doesn't do anything or isn't doing enough to limit the buildup of power by Hamas. Well, one of the assumptions is that Egypt intentionally turns a blind eye. Why? Two main reasons. First, to maintain the status quo with the Islamic movement in Egypt, the biggest political threat to the rule of al-Sisi. Second, to keep Gaza as a bargaining chip with Israel. Although there is a peace agreement between the two countries, Egypt still sees Israel as an enemy.
While the peace agreement prevents a symmetrical war between the countries, but it is less effective in reducing terror against Israel. Egypt can claim that, as is, it has difficulty asserting control over the Sinai Peninsula while facing Islamic State (even though Israel allowed Egypt to bring military forces into Sinai), and therefore, when the question of Hamas is raised, the Egyptians can say "we're doing what is possible."
In conclusion, the buildup of power by Hamas would not have been possible without the help of Egypt, with the regime of al-Sisi and Kamel's organization either actively helping or turning a blind eye. The Israeli intelligence services are not effective in terms of Egyptian territory and the Sinai, based on a (justified) perception that terror in Gaza is preferable to war with Egypt.