Because essentially they are counting it wrong.

They basically put all the revenue into one pot, then divide it by the songs play count.

Which means that account that streams 10 000 plays, have more "voting power" on the revenue that one that just listens "normally"

Because you as a user don't distribute your $15. It's not like if you listen to one artist only, that artist gets your $15. Instead they throw it all into one pot and distribute it in accordance to the total plays. This is why Taylor Swift gets most of your money even when you didn't listen to her. I wish it was different.