As I understand, "blackholing" is basically siding with criminals: attackers want the victim to get off the network, and by "blackholing" the network operator complies with their demand, which allows attackers to save resources. Everybody wins except for the victim.
Normally for DDoS migitation, you blackhole on your normal ISP, and you simultaniously advertise on the mitigator. The mitigator scrubs the traffic and sends the clean stuff over a private session back to you.
If you just black hole and move on, yes that's a lose. However many ISPs will, because the quick reaction holds the most value for them.
