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

[WhyAmIHere]

Everywhere I look it's always "Damage damage damage damage damage".

There's no reason to have a couple extra bits of HP when you need that damage to push phase change or beat enrage it seems.

you have mitigation tools. use them more wisely before overstating the value of TEN as a stat. Everything happens when it will happen, and can have mitigation from everyone mapped accordingly.