Beautiful men are beautiful - worship aspect. Main thing, for me.
Sharing someone's orgasm is intense, primal, intimate - aspect of being very honest, real and "in" with the dude, if only for a brief moment.
Power aspect - maybe, but that would cut several ways. Cocksucker submits - but submits by choice, by his own consent, as a compliment to the top. Cocksucker is powerful & powerless at same time.
Getting the top's load, is a compliment from the top & a sign of his masculine health. I actually prefer the cum-filled guys who shoot fast & might give it again