Loudness war
Two decades of escalation in which records were mastered ever louder, until there was no dynamic range left to sacrifice.
The logic was simple: louder sounds better, at least for the first few seconds in a record shop or on the radio. The CD had a hard ceiling at 0 dBFS, and digital limiters made it possible to shove the average level right up against it. Between the early 1990s and the mid-2000s, the average level of pop music rose by around 10 dB. The high-water mark is usually placed at Metallica's Death Magnetic in 2008, clipped so badly that fans preferred the version ripped from Guitar Hero.
The war wasn't won by engineers but by algorithms. Once broadcasters adopted EBU R128 and streaming services began normalising to a LUFS target, an over-compressed track simply gets turned down to match everything else — and then sounds flat rather than loud.