How? I'm saying that, for me, learning about the universe is its own reward. Because, in this hypothetical scenario, someone is asking me why I care about, say, black holes. They have no practical application to my life at this point.

My response is that learning about the universe is its own reward and things don't need a practical application to be worthwhile. The fact that I'm talking about my own experience is completely obvious when I say learning about the universe is its own reward. Things not needing to have a practical application to be worthwhile is just a logical deduction from the fact that this thing is worthwhile to me even though it's not practical for me.

I'm not "deciding what other people should find rewarding". I'm merely answering the question, "why do you care about this?"