No one is saying they're absolved. Where have you heard that?

The fact of the matter is that if you don't like genocide or gitmo or whatever other horrible things, you should vote for the person who at worst wants to maintain the status quo of horrible things.

That said, Obama wanted to close Gitmo. Biden has also condemned Israel's attacks, and the US has warned them to stop. We've also stopped some military aid to them, but obviously not all. The recent jets, for example, still happened, but they're air-superiority fighters which serve no use against Palestine. We've also continued to send a lot of other defensive aid, though offensive has slowed down if not stopped. To imply Obama or Biden didn't try to do anything is ignorance at best, if not an outright lie. The fact of the matter is that much of it is handled by congress though, and republicans in congress will stop a Democrat from doing essentially anything.