Because it's a heck of a lot better than what some people such as the grandparent are doing, which is ignoring the existence of the Subscriptions view entirely and relying on the home screen to be useful.
Using the Subscriptions view is as simple as changing your bookmark. Setting up RSS is a lot more complicated for someone who isn't already using one.
If you're already on RSS, no one is suggesting you use Subscriptions instead.
I do not understand why people keeps suggesting subscription view, as it is a worse experience for me, than central RSS management