Most readers and fans don't have these kinds of intense discussions when deciding if they like something.

For most people it's:
Barbara as Oracle stories = great
Barbara as Batgirl stories = middling

The same logic applies for Cass and Steph:
Cass/Batgirl = Great
Cass/Orphan = average

Steph/Batgirl = Great
Steph/Spoiler = okay

It's simple logic for most people. Barbara had Batgirl for ten years and didn't do anything spectacular with it. I don't like going back to Oracle either, but at least we have proven results with that mantle. People push for Cass and Steph because their potential for stories in the role far exceeds Barbara's. Look at her overall run as Batgirl - bar Simone, it's nothing we hadn't already seen back in the bronze age.