Because the new system is mostly beneficial for Google, not for the artists. And it only works if a lot of artists cooperate. Instead of offering the artists a better deal than they have now, winning them over, Google realizes that this for most artists this isn't worth the hassle, so they just force everyone to participate. This whole ordeal reminds me a lot of the Google+ integration into Youtube.
A clever, enterprising lawyer would advertise a DMCA service that pummels Youtube for every artist that doesn't want to be blackmailed into participation. Youtube is practicing extortion, pure and simple: "either we own you outright, or you get no money at all." There's no negotiation whatsoever and if Google had thought about this ahead of time, they'd recognize they're opening themselves up to an anti-trust case. Youtube is every bit the monopoly the A&P were and they're effectively dictating their price for all music for everyone whose music is ever used on Youtube.
I get this vibe too.This whole ordeal reminds me a lot of the Google+ integration into Youtube.