You have to keep in mind that these people have been oppressed for nearly 8 decades. Israel is actively trying to make it so they literally do not exist anymore as a people.
There's only one way to keep a community alive in the long term, and that's by continuing to have children in an attempt to continue existing.
There is a reason why Gaza's population skews so young. When they're murdering all of the adult men, they're going to need to "replace" them, or else their people will be completely removed from existence.
Yeah, but that's exactly what Israel wants them to do.