I'd assume it's to keep things easier, especially for a young company. It should be much easier to deal with publishers when you can agree on cost per view, rather than trying to work out some magic subscriptions share model, like the one used by spotify, which is pretty hard to do and keep everyone happy.
I agree, but that variable cost is what makes it variable to the consumer which is generally not accepted. Putting a hurdle before a click to view an article generally destroys your readership.
It's totally true for things like spotify, where you can easily stream thousands of songs just in the background every month. Imagine how silly it would be if you had to make sure that spotify is closed when you leave your computer on for some time :)
However, consuming written content is different. It's much more involved, conscious action. So I am not sure if it is really much worse for the user.
But that's just an educated guess :)