Stylistically, pop has changed significantly even in the past 10 years. Going back 20, the differences are even more striking. Of course, chart-topping pop songs are mostly very manufactured, but that's been true for 100 years.
Rock is no longer a "mainstream" genre, in the sense that rock acts generally don't top the charts or occupy a large space in the zeitgeist (hip hop has replaced rock in this area). But I think this has been healthy for rock; the genre is now more fractured, and as a result, more varied and experimental. (Don't @ me metalheads. I love metal too but it is not a mainstream genre)
Sorry if that got a bit rambly -- just wanted to point out that there is tons of evolution in contemporary music. It can be harder to see that, though, since music streaming has taken a big chunk out of the music monoculture. That means finding interesting music is more accessible, but requires individual effort to seek out (and the sheer quantity can be overwhelming).