You're referring to survivorship bias and yes, that's a factor. But while there was a fair amount of garbage topping the charts when I was a teenager, there was also a fair bit of great songs as well. For a variety of reasons, the selection process of what becomes a chart-topping "hit" has changed, and I think that is part of the problem. The biggest factor is that the business side of the industry has virtually perfected cramming what they want into our ears until we like it - or at least until they make money off it. In the past, society as a whole mostly selected the winners through tuning into radio stations, buying albums, etc. The nature of the business has changed dramatically over the decades where now people just pay for streaming services which for all but a few artists never come close to replacing the income they would have had via the older methods. The industry execs have also gotten really great at manufacturing pop hits through people like Max Martin (and the other guy who's just like him) who crank out similar/familiar songs with the same structure over and over so people like it because it feels like they already know it and it's so close to something else they already "approve" of in their brain. It's the music industry equivalent of how social media hijacks your dopamine system.