Egypt has refused to implement U.S. peace proposal for Gaza, that would halt the smuggling of weapons into Gaza via tunnels under the Egyptian border. The Egyptians officially say they will stop the smuggling, but they have been saying that for years. In practice, the Egyptians are not willing to take the heat, from their own pro-Palestinian population, and from the Bedouin tribes in the Sinai desert around Gaza, if they actually cracked down on the weapons smuggling into Gaza.
Then there's the bribery among Egyptian police and border patrol officials in the Sinai and the Gaza border. The Egyptian civil servants consider bribes as a necessary fringe benefit, they only way they can make a decent living on their low civil-service salary. But the big problems are political. The government, which is a police state dictatorship pretending to be a democracy, survives by not antagonizing the population too much. Putting the hurt on Hamas, who are Palestinians as well as Islamic terrorists, would not be popular in Egypt. In return, Hamas does not support Egyptian Islamic terrorist groups.
Then there are the Bedouins. They consider it their right to smuggle. They make a lot of money smuggling weapons, and other goods, to the Gaza frontier, and own some of the tunnels going under the border. The Bedouin also smuggle drugs and people into Israel (but avoid a big crackdown there by staying away from terrorism). Whenever the Egyptians try to crack down on the Bedouins, the Bedouins go into terrorist/guerilla mode. Sure, the Egyptians can crush the Bedouins, but that creates diplomatic problems with the Bedouin governments in Jordan, Saudi Arabia and throughout the region. So it's safer to let them smuggle, and be friends. Comes in handy when Islamic radicals try to operate in Bedouin territory.
But the U.S. does have some leverage. Egypt gets $1.3 dollars a year in American military aid (and nearly a billion dollars worth of economic aid). Egypt has received over $50 billion in U.S. aid since the 1979 peace deal between Egypt and Israel. The large amount of aid was part of a deal to get a peace deal between Egypt and Israel. A bribe, if you will. No one has tried withholding that money as a way to influence Egyptian behavior. Perhaps because it's not a sure thing that the Egyptians would take on the Bedouins, Egyptian public opinion and their own corrupt bureaucrats, even if the U.S. stopped sending all that money.