What do you guys think is the cause of severe lack of Tank users?

[Vyrerus]

It has always offered additional enmity. Its modifier was just significantly lower, as if more to compensate for the damage loss (via modifier and the loss of Sword Oath) inflicted rather than being an "enmity stance" per se, such that wielding a dagger in Sword Oath could quite possibly out-enmity Shield Oath in single-target (since, back then, Sword Oath's bonus potency didn't scale with weapon delay), while they were otherwise relatively neutral. This was quickly buffed.

Yeah, Shield Oath did, but not Defiance.