Why is the Rafah border crossing closed to Palestinians?

I've been trying to understand why Egypt is keeping the Rafah border crossing with Gaza closed, and the best explanations I have found are this one from the BBC, and this one from Time.

It's hard to believe, but there are only three ways out of the hell that is Gaza: the Erez and Kerem Shalom crossings in the north, which lead to Israel and almost certain death; and the Rafah crossing in the south, which leads to Egypt and a slightly lower certainty of death. Since Hamas took control of Gaza in 2007, Egypt has cooperated with Israel in enforce its blockade of the Palestinian enclave, partly because it feels it is also in its own strategic interests. Israel also restricts access to and from Gaza by air and by sea (not to mention that millions of tons of raw sewage ends up in the seas along Gaza's short coastline since its sanitation system broke down, so it is inadvisable to even try swimming away). Gazans have effectively been prisoners in their own land for decades.

Currently, Egypt is keeping the Rafah crossing closed, and thousands of desperate Palestinians are waiting on the Gaza side hoping to escape Israel's bombardment and the upcoming ground attacks. Meanwhile, there are reports of several Israeli air strikes on the trapped Palestinians waiting to leave. In theory, foreign passport-holders should be allowed to leave through Rafah, but in practice there are many hold-ups. 

On the Egyptian side of the border, hundreds of trucks carrying desperately needed aid are being held up, with many more arriving every day.

The official Egyptian line is that the crossing s technically open as far as they are concerned, and they are blaming the Israeli aerial bombardment for making the crossing too dangerous to allow aid convoys to cross. But the truth is that the Rafah crossing has never been very open, and Egypt has kept very tight restrictions on it for many years, to the extent that they actually seem to be bolstering Israel's blockade of Gaza.

Egypt may be another Muslim-majority country, but there is nevertheless no love lost with the Palestinians. For one thing, they worry that Palestinian insurgents may link up with Al Qaeda jihadists already operating in Egypt's North Sinai territory. 

But, probably more importantly, they just don't want into open up to a mass migration of Palestinians into Egypt, for which they would then bear responsibility for an indefinite period of time. Even less do they want to see a permanent resettlement of hundreds of thousands of Palestinians in their land. They certainly do not want to give the impression that Sinai may be considered an alternative country for Palestinians.

Negotiations are currently under way for a deal to open up the border crossing and allow safe passage for many thousands of beleaguered Palestinians (and to allow aid in to Gaza). But don't expect the Egyptians to make it easy.