I've met Richard Petty. I've talked oil with Richard Petty. He doesn't know nor care what's in STP. They just hand him a check. They funded his racing program, that's it. I doubt he ever used the stuff.
How many people are knowledgeable and experienced enough in lubrication and engine wear patterns to find, acknowledge, and properly conclude the root cause of engine sludge, damage, etc...? Very few. Even many reputable engine builders can't do that. If the consumer thinks STP is doing them good, they'll never even consider it being the cause of any issues they may have. Marketing/advertising goes deep into psychology. There's a reason it's a multi-billion dollar industry. Good marketers know how to get inside your head like they seem to have done with you.