Why don't people like to pick/use Tenacity over Determination?

[TheForce]

Because there’s no reason to. Kill the boss faster to take less damage and DPS checks sound over tuned. Again.

Outside of progression there’s no real reason to have it and even then that’s a maybe.

Hmm, I disagree with that stance, your damage intake only matters as long as the boss is alive, imo you can't really say that the boss's death is mitigation. The moment the boss goes down, it's a totally different situation...