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

[msoltyspl]

I'm someone that's fairly new when it comes to tanking and I don't think I've had a full explanation as to why its not used much. I noticed some people complaining about the new Eden gear having Tenacity over Determination.

Anyone care to explain both their differences and why one is used over the other one to me?

In terms of having the same boost of damage as from some tenacity value, you need only 70% or so determination. The issue with tenacity is that its mitigation is in practice not something making real difference - so the tradeoff has little sense. It's essentially dump-into stat as soon as you filled up the rest and reached your desired sks tier.