I have no idea. I found this older topic about PlaceIt: Placeit Joins Envato In good old Envato style no direct answers are given, actually no answers at all are given. It seems like there might be external music in a buy out, but again I have no idea.
PlaceIt have been in the bottom of the marketplace pages a long time and also in the tiny “quick links”, but this new prime time placement is a strong indicator that Envato wants to migrate market customers there as well.