As a Tank my DF pops instantly. Never have an issue with it. Its all about supply and demand, as the others have said. Tanks are in short supply compared to the amount of DPS classes. Healers are also hardly available. While I don't agree with it, a tank can pick and choose his DF groups. If he doesn't like his group, he can find another fairly easy. A 15 minute penalty is not very long for us, considering the DPS wait times.

What people should be asking is for SE to try to make tanks more desirable. While I love my class, not everyone shares my love.