In order for the smuggling at Rafah to take place, all of the weapons and explosives have to cross the Sinai. Furthermore, Egypt has not even tried to hide the fact that it has allowed free movement of known terrorists from and to Gaza, in violation of tripartite agreements. You are also correct to say that they have weapons that they do not need.
U.S. Democratic Senator Merkley airs support for Iran nuclear deal (Reuters)
from the article: Egypt FM: Pro-Israeli lobby is harming our relations with U.S.