>>12333622To start, he was only really over with the internet smark fanbase, which was smaller, but even smellier than the one that exists today (and of course, braindead Chicago crowds). Paul Heyman also had a hard-on for him, which helped him during his early days in WWE.
During the SuperCena era, fan resentment towards WWE booking ended up manifesting in support for guys that they thought weren't being treated fairly, and that combined with the pre-existing smark support for Punk. Then, the pipebomb happened, which finally got him over with normies.
That kind of support never lasts, because people don't want to support the underdog when they're no longer an underdog. He had an insanely long title run, but no-one cared at that point.