[artwr]

Illegal downloads surely had an impact in the 2000s era, but I think by now the amount of freely streamable content is by far the largest factor.

[intended]

Unlikely - streaming expanded the market for music.

I recall a report that showed that p2p networks acted primarily like a broadcast medium, which tuned to the most popular works.

The entire free content model has arisen because of tacit acknowledgement of that fact.

Youtube, hell everyone, applies those lessons today.

[EADGBE]

And, as I pointed out originally, there was about an 8 year gap between demise of album sales and the prominence of streaming.