Tbh that's literally every decade/generation where they complain about the current state of music being trash, so that's not what caused Best Buy to stop selling CD's. Also that can also be applied to every form of media where there's a ton of people saying the current (movies/games/whatever) is hot garbage and the classics are the only ones worth checking out.
What I think caused Best Buy to stop selling CD's is that they noticed waning sales, so they don't stock as many CD's, and this also in turn causes customers to stop looking at Best Buy for CD's. MP3's and Spotify are what caused people to not buy CD's anymore, and now buying albums is relegated to being a niche hobby, as the average person doesn't care enough to listen to full albums anymore.