Can you shoot some examples of what recorded music you're thinking of?

I think what you are referring to is that the recordings we have today of music are from Vinyl records or even older technologies, these things added a hint of background noise to the the sound. I think its actually white noise you are referring to. Basically its just poor sound production quality, and there's no way of going back and recording old music with good equipment.

If that's not what you are referring to then its probably because culturally music has changed a lot over the past 100 years. Both in style and in how it made it to the masses, and more importantly the scale and frequency of how that happened. The sheer volume of music produced today makes a 50 years ago look small.