Squad writes "A decade ago they were a dominant force in gaming. There were always a plethora of tower defense games being offered, including classics like Plants vs. Zombies and Iron Brigade. Even some famous franchises – such as Final Fantasy – dipped their toes into the tower defense genre."
You got it backwards, it's more popular now. Also you show zero statistics to back up your premise.
Pixeljunk monsters was one of my most played games.