This is a widespread misunderstanding; there is no border anymore between Gaza and Egypt, as it was occupied by the IDF in the first year of this war. So unless Egypt went to war, there was nothing they could do.

And even before this war, the peace treaty gave Israel big control over the Rafa crossing. They have a camera and watch everything going in and out, and can ask for extra searches if they don't like what they see. And in all, it's just for individuals, not cargo. Whatever cargo goes through, there is just a limited amount that requires prior approval from Israel.

So Egypt really doesn't have any power over the situation unless they are willing to risk a war, which they can't win.