Black Sabbath - Born Again 2011 Deluxe Edition

Upon listening to the 2nd CD of the concert -
the fans were - amazingly welcoming - of Ian Gillian.
I thought about this - I've never heard of a replacement musician - so welcomed.
Esp. a vocalist.
The crowd was singing along with him too ! The happy vibe !

I was even excited, way back when, finding out Ian had joined the band.
Not seeing that concert - ooohhhh depresses me.
My friends went, but didn't ask me along. Sigh.
But I did see the Perfect Stranger tour - a year or so later.
Any thought on why Ian was embraced instantly by fans ?