humans also don't grasp death on any deeper level than AIXI. They also drop anvils on their head so to speak

If human adults didn't grasp death any better than AIXI does, they'd routinely drop anvils on their heads literally, not 'so to speak'.

This is for the same reason AIXI does. Symbolic reasoning about reality.

What do you mean? What would be the alternative to 'symbolic reasoning'?

The body provides the 'reward' button. And that button can be hacked (drugs, optimizing for single values).

If a smart AI values things about the world outside its head, it won't deliberately hack itself (e.g., it won't alter its hardware to entertain happy delusions), because it won't expect a policy of self-hacking to make the world actually better. It's the actual world it cares about, not its beliefs about, preferences over, or enjoyable experiences of the world.

The problem with AIXI isn't that it lacks the data or technology needed to self-modify. It's that it has an unrealistic prior. These aren't problems shared by humans. Humans form approximately accurate models of how new drugs, food, injuries, etc. will affect their minds, and respond accordingly. They don't always do so, but AIXI is special because it can never do so, even when given unboundedly great computing power and arbitrarily large supplies of representative data.