The fundamental claim of the RIAA is that all this royalty money is required to encourage artists to produce more creative work.
However, most audio recording artists retire from creative work after only a few successful years.
The retire on the exorbitant royalties of their work. (They may continue to perform, but merely preform what they have already created. And while there are some exceptions, these exceptions are motivated to create by something other than money: perfecting their art, communicating with people, or fame.)
This contrasts with successful painters, sculptors, and broadcasters, who generally continue creative work their whole lives.
It is an example of what economists call the "backwards bending supply curve of labour".
1. In general, pay workers more per unit of work and they initially they work longer.
2. Once workers have most of the material possessions they really want, they start to purchase leisure time: Workers use their increased rate of pay to reduce the duration of their work they do.
In other words, exorbitant royalties cause most audio recording artists to retire from creative work after just a few years.
(This is starting to apply to the medical profession in many countries. Pay your physicians and surgeons enough, and you will see them start to spend more time on holiday.)