This was so interesting. And surprisingly empowering.
TL;DR: It's our fault. But that means we also have the power to demand better music.
It's not just you; much of pop music really does sound the same. A study done by the Spanish National Research Council produced these graphs showing the increasing loudness and decreasing timbre of pop music over time.
Many people (me included) assumed that music was getting "worse" because record labels and mega-corporations that compose The Man were making it so by pre-selecting in some dusty Hollywood or New York City boardrooms what hits would go on heavy rotation on the radio.
Little did I know that with the advent of music streaming services like Pandora and Spotify, another, more sinister force would ruin popular music. Who is to blame, you may ask?