Unpopular opinion but he's a whole ass grown man, Myrna put in her time.
She's as crazy as he is, only she's fortunate to have married well and not ended up like Lucas.
She SHOULD do more to help him just because, but she's not legally required to do so.
I agree with your first sentence, but not the rest. Myrna is NOT as crazy as Lucas, that is just objectively false. Myrna really does not seem like a great person or mother, but she is by and large pretty normal. She is narcissistic, but that's about it. She has had TWO men love her enough to marry her, she retired young like Lucas always brags about, and she owned and managed a business. Also, her other son Seth (Shawn is his dad's from a previous relationship) is normal and doing well as a teacher. She definitely coddled Lucas more than she ever should have, but especially when he was a child, I can't fault her too much for that. No one wants to see their kids struggle to fit in and make friends, and of course she would want to make him feel better, From when he turned 18, his family tried to get him out on his own and draw hard boundaries, which they have, for the most part, stuck to. I don't LIKE Myrna by any means but I feel like people in this thread are too hard on her, I feel like everyone in Lucas's family are really normal folks who did their best with the beast they were stuck with. Lucas was doomed from the start, his mom being sad for him that he wasn't normal isn't what fucked him up. Myrna's actions were a RESPONSE to Lucas already being a braindead fuck up.
Now, that doesn't make it okay that once or twice a year she acts like she gives a fuck about him to make herself look better, but she is an exceedingly average woman who doesn't and never has known how to cope with the utter monster that she bore. Lucas's parents have tried to help him many times, including setting him up in places to live, and he trashes the place, doesn't pay rent on time, or does something else to ruin it. You are absolutely right, he is a grown ass man and he is a horrible excuse of a human being. I don't blame his family for giving up on him. I also don't think that Myrna (or Roy) "should" do more to "help" Lucas. The only reason I would say that MAYBE they should is for the benefit of the world who has to deal with the revolting monstrosity that has become of their child, but for Lucas himself, "help" doesn't help him. Like others have said, the only thing that would help him is an old fashioned sanitarium where he is locked up as if in prison, and HEAVILY medicated for the rest of his days.
Myrna also didn't just "get lucky and marry well". From my understanding, she and Roy built their travel agent business together, and then Myrna kept it after the divorce and got her new husband into it with her. She worked hard to have a decent life. Like I said I don't LIKE her and I don't want to seem like I'm just blindly defending her, but I really don't think it's fair how much she is blamed for Lucas being Lucas. Lucas would have been a bipolar, schizophrenic narcissist no matter what kind of parents he had. Maybe Myrna's coddling sped up the narcissism a bit, but he is what he is because of his vast mental problems and because he himself is a shit human being. From what we know of his family, none of the rest of them seem to be flat out bad people the way he is.