The shield itself is not important. That was just used in the screenshot since it was the item dropped from the last boss.
Meaning that I could take the screenshot like I did, without wasting the groups time doing so.

I didn't want that shield, I couldn't care less for it since it was clearly for a caster. So I had no intentions of rolling need on it.

The question was about the greyed out need button, since I didn't get that the game displays all classes that in theory can equip the item.
Had it only displayed the classes that would actually benefit from the stats, the casters, I would never had thought that I had stumbled onto a bug or may have changed something somewhere in some options by fault that made it so that I couldn't roll on gear at all.
Especially since it also happened on all other gear drops in the instance that either displayed GLA or disciple of war on them.

I even asked the group about it, and they couldn't give an answer so I came here.