My mom, who was my very best Disney buddy, is in the end stages of dementia. Every now and then, I mention to God that if he'd just change things, the first thing I'd do is buy tickets and hop a flight to WDW.
People are selfish. I've got it in my own family with the sibling and his children, who we took with us when they were young children.
I can't think of anything more important than family relationships but they require sacrifice and some people just don't have it in them to sacrifice their time or attempt to accommodate anyone else, even family. No doubt, it's hurtfull.
About the OP and the others with similar situations, I feel sorry for your parents. They're missing the opportunity of a lifetime.