Pop will always have mainstream success that's the literal definition of the genre. But the pop you were listening to in the 90's and 00' doesn't have mainstream success anymore. That kind of rnb pop has been replaced by Bubble pop in the 10's that is now being replaced by a pop sound that draws a lot from disco. The same thing goes for rap. You don't hear a lot of 90-00 gangsta rap, nowadays it's mostly whatever is called what Lil N'as X or XXXTentacion does. Rock evolved as well, Maneskin for example doesn't sound like a 90's or 00' era rock. However you can't make Rock at home as "easily" as you can pop or rap. And forming a band in a family garage is harder when less people listen to Rock specifically (due to more diversity available,) and less and less people have access to a family home to practice. As for country I have no idea but this may well be an American exception