Egypt has the second largest debt in the world (after Ukraine).
They don't want to open the border and be responsible for the care of so many refugees - they can't afford to and the influx of so many will cause internal tensions.
There has been some speculation that one of the reasons they've not opened the border is because they are looking to use the opportunity to strike a deal with the US for debt write off and assurances over aid. There's also been some suggestions that they have been putting up barbed wire fences close to the border in preparation for the border opening so they can keep the Palestinians there. They also have certain limitations on what activities they can do in the area - they need approval of the Israeli government (because of historic issues).
In fairness to the Egyptians all opening the border would do is effectively 'shift the problem' onto their land. What happens in 10 - 15 years time if something happens again from this area and Israel are upset? Do Israel attack Egyptian land to 'deal with the Palestinian problem'?
The Lebanese government doesn't effectively control the whole country due to areas being controlled by Hezbollah. Egypt also risks this, if they open the border.
So it's easy to see why even Palestinian sympathisers have reason to be reluctant to help in practical terms with humanitarian assistance and opportunities.
The cancellation of the Biden - Egyptian meeting has to be seen through this lens. Egypt wants to up the pressure on the US because the optics of the hospital bombing (which frankly was inevitable one way or another due to the density of Gaza - a similar incident was always likely to happen and it illustrates why Israel acting aggressively in response to the attack was never going to end well). The US is isolated internationally in many respects on this even though the UK generally has always been sympathetic to Israel.
The UK government has said they believe there are about 60000 British citizens currently in Gaza. And any response the UK government makes needs to be seen through this lens. We are much more likely to have protests here due to the sheer number of relatives living in the UK.
I did think that the UK response of flying the Israeli flag after the attacks was essentially ill judged for that reason. It's not reflecting changing demographics and public sentiment. It doesn't help us and it doesn't really help Israel in the long run.
The pressure on the US to sort out the whole sorry mess and inject some rationality into the Israeli government is intense. The comments from Israeli about 'tent city' or 'killing them all' are deeply problematic.
I don't know that they can sort it out.
A lot of people are going to die. The hospital bombing is just the start. Unfortunately.
No one wants the Palestinians. No one.