historically, any sign of growing support for left wing groups was shortly followed by whipping up a group hate on catholics so the unionist leadership didn't have to share power with anyone. they had a great line in convincing w/c protestants to play the turkey woting for christmass and reject having any real influence themselves so catholics didn't get any either. following that, the DUP was the first party to significantly focus on the rights of w/c protestants and they played the loyalist card to the full.
so socialism has been linked with disloyalty, with nationalism, it's a dirty word, so you end u with groups like the PUP as progressive unionism that are supposedly left-loyalism , cause they can't call themselves anything that's not demonstrating loyalty.
so with mass politics being like that in protestant areas, they are few and far between and need to reject a lot more inbred bullshit. there have always been some though, like a few protestants in the INLA. but most of those not willing to completely cross the line know to keep quiet