I hate failing in non PUG raids. I think I'd leave on my own if I managed to fail at something (like soaking shadowfel burst).
There's also the factor that you can probably blend in easier in fights we haven't done on heroic our self. I'd have to, at the very least for my own peace of mind, do research of what is different on heroic.
And even if I DO have more control over the success I don't want to have to cover for idiots. I mean I probably would do fine in a PUG, but just to be safe I spare my self the possible "trauma"
Much like I have not done PvP for like AGES.
I mean like I think I might have only done the BG NEEDED to complete the legendary cloak quest line in MoP for the last 2 or 3 expansions. And if I were to do any BG, it'd be Alterac Valley for sure! PvE PvP FTW!
And then lets start raiding again! We'll just have Spoisen conjure us up a couple of healers and DPS and we can have social aspect raiding again!