I used to spend a lot of time with my grandparents as a kid. As I got older and into school, I spent a lot less, which I now kind of regret. If Ketch's mom wasn't close with them, I could see that relationship fading away once he got out of the toddler/little kid stage and into the preteen/high school/college age.
As I've gotten older, and especially once I became a parent, I've begun to value time with my remaining grandparent much more. I think this is probably a natural occurrence as we mature and start to appreciate mortality. We see that we only have so much time left with certain people and that placing an importance on other things has been a missed opportunity with some of them.
Personally, I wish I'd have spent more time with my grandfather before he passed several years ago. It was unexpected, even though he was getting on in years. I even don't mind spending more time with my wife's family. I know her grandparents don't have forever, and they enjoy spending time with my daughter. I also want her to be able to remember them. I think being a (not ****ty) parent gives you a certain perspective and appreciation for family and the time you spend with them. It wouldn't surprise me if Ketch felt the same and just wanted his twins to know who their family was and wanted his grandparents to know their great-grandchildren.
I also used to spend a lot of time with my grandmother on my dad's side. When my parents got divorced, I hardly saw her anymore. I barely knew her when she passed away, but I remember spending weekends at her house and listening to get play piano and playing cards games with her. I even spent a lot of time with and was close with some cousins on that side that I haven't seen or spoken to in 20 years. I was even at A&M with one and never saw her. I don't think there's anything suspicious or irregular about losing touch like he says he did.