On what basis do you claim that humans bother to experience happiness,

I would think that he claims that humans experience happiness, because humans do in fact experience happiness. That seems like one of those questions that is, and remains under almost all circumstances, very simple.

Edit: More prosaically, humans experience happiness because that's one of the adaptions that we evolved.

as opposed to "just" outputting the action that leads to the most expected apeyness?

And humans aren't ape maximizer. Human evolution is an ape maximizer (sort of), but humans are "just" adaption executors. It's evolution's problem that said adaptions have stopped working (from its perspective, anyway).

Aren't you just as much a ghostless device?

Everything is a ghostless device. That's the point.