Häh? The sub is optional? Is it? xD That's just not true.

And the reason why they don't increase the sub price is very easy.
It already IS very expensive. And at the same time they deliver less and less new longlasting content and stuff.
When they increase the price, when, at the same time, they deliver less and less content, u know what will happen.
People go away. In the end it's just business.