Where would they go to, not like we have a choice in utility providers, you would have to move?
No...the law requires a choice in those cases. What happens is that the same gas is sent down the pipes, but the credits are issued through another provider.
Kind of like electricity. I live in Anaheim, with my electricity provided by the city of Anaheim...not Edison or anyone else. Now Anaheim doesn't actually make or distribute the electricity, they merely buy 'time' from someone else and resell it to their residents. A benefit of this is that we NEVER have rolling black/brownouts.
Anyhow, the customer exodus was largely due to PGE's recent financial support of the homosexual agenda using taxpayer money. Christian (and some non-Christian) buyers found this use of public funds idiotic and left.