It may well be that JMo and GG aren’t fan friendly when they’re on set. You don’t see pics of fans with them the way you do with the other actors. But if they don’t feel comfortable mingling with fans while they’re working, they’re not obligated to, and shouldn’t be bashed because of it.
There’s a saying that you shouldn’t bite the hand that feeds. VCF has built their reputation on basically exploiting everyone who works on not just Once, but other shows as well. I’m not gonna say they’re evil for doing that, because it’d be hypocritical considering how enthusiastically I devour spoilers, many of which are supplied by VCF. But speaking for myself, if I was using these actors to make me who I am, I wouldn’t go around badmouthing them in public, (if they’d been genuinely horrible to me personally, I’d diss them in private to my personal friends, but I think it’s poor form to diss them publicly just for not doing something they don’t actually have to do).