Check the ingredients in that chocolate, and it will probably have something called "PGPR" in the list. PGPR is a flavorless, odorless, waxy solid with a similar (but not identical) melting profile to cocoa butter. Now cocoa butter is expensive and getting more expensive, and companies like Reese's, Cadbury's and a lot of others just started cutting much of the cocoa butter out and added in PGPR as filler.

That's just one way these products became flavorless, waxy, and generally unpleasant. Of course to combat this more sugar is often added, just to keep people coming back. More broadly though highly processed food is just too salty, too sweet, and often has a background of off-flavors... but it takes time away from them to start noticing it.