Parents who work full time have limited time with their own children.
Presumably the children also have activities, play dates and appointments that cut into that precious time.
I can see why they don't want to spend the precious little time they have with their children every week, running around discharging their perceived obligations to relatives.
10 miles isn't just down the road. It's 30 min there, 30 min back, a visit for two or so hours in between. There goes a whole morning, which might have been their only time to spend as a family. I think that's asking too much on a regular basis.
If you drive, I suggest you offer to visit them, whenever suits them. Then the parents can still relax in their own home, or attend to the chores that built up during the week while the grandchildren spend time with you.
If your DIL is a social worker, I doubt she's a selfish entitled person. She's chosen a difficult profession that focuses on other people's needs. There might be some compassion fatigue at play as well- she spends her whole week tending to needy people, I can see why she doesn't want to devote half her weekend and her family time to it as well.
If you want people to spend time with you, be positive and flexible- make it a joy not a chore or obligation.
My PIL were massive on the guilt trips if we didn't see them at least once a week- it made seeing them a chore and damaged our relationship.