OP, I can appreciate the sadness of your post and I can read that you are taking it personally.
What I have realised through getting older myself is...
I have teenagers but am so over young children. I have absolutely no interest beyond a 10 second smile and "isn't he/she cute".
Young children can be really exhausting as you get older.
Neighbours with grandchildren have told me that although they adore them, they have to leave their homes to get a break and a rest from their children constantly calling on them!
That even though you might love them, long visits are tiring.
It's much harder for grandparents to keep children safe than it is for parents. Parents can almost have a second sense with safety, grandparents can find that harder.
Mentally grandparents can find all the chatter exhausting, even though they love them.
If your parents already have a lot of contact with their other grandchildren, maybe they have had enough of it.
I know my darling SIL loves the bones of her grandchildren but she finds the constant daily visiting of them with her daughter's utterly exhausting. She wishes she could have a couple of days a week where they didn't visit and use her home as central station. She adores her daughter's but won't say anything.
It's really unfortunate that they weren't patient with your children but instead of thinking they don't like them, maybe accept they just aren't able for them.
Wishing you the best💐