I don’t think there were any changes that NASCAR made that affected driver safety that drove off any fans. What drove off fans was changes like an abundance of 1.5mile tracks, race locations, scheduling, competition cautions, the playoff system, stage racing, and messing with the engine package in the cars.
The way the NCAA is losing popularity is by literally not enforcing any of their own rules, and allowing just a few teams and schools to dominate even after years of rule breaking. Also, by seeing the regionalization happen in college sports and actively doing nothing to prevent it, or help spread the wealth and success to different parts of the country.