At a certain point Moore's Law died and that point was about 20 years ago but fortunately for MP3s, it happened after MP3 became easily usable. There's no point in comparing anything before 2005 or so from that perspective.

We have long entered an era where computing is becoming more expensive and power hungry, we're just lucky regular computer usage has largely plateaued at a level where the already obtained performance is good enough.

But major leaps are a lot more costly these days.