Maybe some kind of increasing scale for revenue depending on larger numbers of listens.
My break down by track is pretty inconsistent, too. I've got a single track with over a million listen that made me 36 cents. My most popular track has over 4M listens, and it's responsible for half that $45. Distrokid doesn't say which streaming service that revenue comes from, either. Some pay more than others, I imagine.
It's not supposed to do anything. It is literally a "tap" on the screen.