Why hasn't Hamas built a more prosperous Gaza?

Briahna Joy Gray said in this video:

Israel is already saying that zones that are supposed to be safe zones for civilians are not in fact civilian zones and that they have been infiltrated by Hamas, that's hospitals, that's camps, schools, refugee camps and the like. So why should anybody take their word for the idea that if there were a bomb shelter, it too wouldn't become a target under the justification that Hamas is using the bomb shelter?

Norman Finkelstein said in this video:

If the United States would send 3.8 billion in aid to Hamas for its military, then they would have money left over to build bomb shelters. Now, you might find what I just said factious. Under international law, an occupied people have the right to use force and violence to end an illegal occupation. Under international law, an occupying power doesn't have the right to use force to preserve an illegal occupation. So under international law, the 30 billion dollars that Barack Obama gave to Israel over a 10-year period should have been given to Hamas because they're resisting an illegal occupation.

That's the law. It sounds funny almost like I'm trying to score a debater point, no. Under international law, nothing is barring a foreign power from assisting people engaged in a war of self-determination. So, President Obama would have been completely in the right to allocate 30 billion dollars over a 10-year period to assist the Palestinians in their struggle for self-determination. However, international law does bar an occupying power from using force to deny a people the right to self-determination. If you are so upset by the fact that Hamas is devoting resources to building tunnels which are used for military purposes that we can agree on, if he's so upset that instead of building bomb shelters, there's a very simple solution, let the unites states pay for building the tunnels which are legal under international law and then Hamas will have resources left over to build the bomb shelters.