Because they would rather die for the land that’s rightfully theirs rather than leave because it makes you or some other people who have no idea what the situation is on the ground more comfortable.
In fairness, while I disagree with a lot of their viewpoints, I think this is a little unfair.
They're not coming at this from a perspective of what they think is morally right but what may just end up being the best thing for them with regards to their actual day to day living.
I guess the similar recent parallel (obviously not exactly the same) is NK and Armenia/Azerbaijan. Is it fair what's happened there? No. Is it moral? No. Will anyone ultimately do anything about it? No. What did most of the ethnic Armenians end up doing? Ultimately they've left (whether by coercion or not, I don't know enough to say) because they've deemed their lives to be better if they leave, rather than continuing a fight they've likely calculated they cannot win.
Of course, a major difference is that they have a 'homeland' they can go to still etc etc.
One thing
@2cents mentioned before which really resonated and I think is true is that the Palestinians (as a collective, obviously there are always different viewpoints) don't see themselves as a few million Palestinians against a few million Israelis, with no out. I think part of it is that they see themselves as a collective, whether as an Arab collective or Muslim, that will eventually come to help in some way, whenever that may be.
Now that may have been true in the past.....but is increasingly not. In fact, its further away than it probably has been at any point since the conflict began. So the ultimate question becomes....what is their out? To a decent and dignified life?
That is a question that I sadly no longer have a viable and realistic answer for.