I always figured it had something to do with the seat, and maybe the T-2 had one before somebody in authority decided it was too risky. My opinion is that it was a laziness issue, not an engineering issue, to simply build a frangible hood that wouldn't obstruct the seat on its way out.
We didn't use a vision limiting device the whole time I was instructing (up until 2018). I'd take my students into the goo any chance I could get. If there was convective weather then we probably weren't flying anyway but if it wasn't convective then I'd be all about getting them IMC time. That did put a lot more burden on the instructor and having a good mental playbook of the local flying area was necessary if you were going to do it safely and in a way that the student could learn the most.