A scientific analysis of a database of over a million songs produced since 1955 has found that modern popular music is louder and has less variety or range than the popular music of the past. Key quote:
Lastly, the researchers detected a trend of homogenization of the timbral palette. Timbre is what makes a particular musical sound different from another, even when they have the same pitch and loudness. It is essentially the difference between different instruments playing the same note at the same loudness. They found that, after peaking in the mid 60s, timbral variety has continued to narrow.
This confirms a suspicion of many fans of modern popular music, that it is less interesting and shows far less creativity than the popular music of the 1960s. This result might also explain why 1960s music remains so popular.