It's a question of visibility. Before streaming we bought the product once and played that media multiple times at home. None of those plays would be visible to the world in general. With a large proportion of the populace preferring to use a streaming service for those multiple plays, then each play is visible to the outside world. By basing the charts on the number of plays then we are no longer comparing like with like.
If they really wanted to compare, then they should only use first plays from a customer for a chart basis. One could also argue that payments to artists could be made on the same basis, given that nobody paid an artist more for an LP that got played 100 times over one that got played once or twice. I'm not saying I agree with that though.