Ah fair enough, I misunderstood. I agree doing things for the sole reason of being virtuous doesn't make sense.
Although I do think the origin of "virtue" is because some things had good general effects, but nobody was able to explain why or how. Of course the concept has been abused since then.
Some societies found it virtuous to kill anyone not of the right race/religion. Some societies found/find it virtuous to genitally mutilate women.
I'm not sure we can come up with a principled way to distinguish the "good" kind of virtuous from the "bad" kind of virtuous without just deciding by ourselves what is virtuous and what isn't, at least to some degree.
Although I do think the origin of "virtue" is because some things had good general effects, but nobody was able to explain why or how. Of course the concept has been abused since then.