These were really mainstream back in like 2011, in fact my first paid campaign that made me really happy was a car insurance offer (the Comparisons.org one) so I still have fond memories of that.
Once heavily popualated with zip submits and full forms, I noticed within a few years after that, the CPL offers were drying up big time on the general networks I was with, though for a while they were being replaced by Pay Per Call.
It seemed like a pretty sudden shift, so I was always curious if something happened behind the scenes that made these offers so much harder to find?