Shouldn’t billing address and payment be combined?

Currently designing an e-commerce website and doing a lot of competitor analysis.

One question that bothers me is why most websites combine shipping and billing information? Most importantly, even if they offer Paypal as a payment method.

It's usually 3 steps: Shipping & Billing > Payment > Confirmation
I understand that billing information is important for an easier transaction when using Credit Card as a payment method (Address Verification System). But is it necessary if I use other payment methods? Should it not be combined with Payment (only when Credit Card payment is selected)? Maybe there are some other reasons I'm not seeing, but this really confuses me even as a user.