I dunno Jennie...it seems to be a natural process in my family...
your grandparents are there for you when you're a kid then as you get older you start to build your own life and they expect to see you less.
My favourite grandmother started telling me...it's a long way for you to come...wait til you have free time' so I did.
I probably saw my grandmothers maybe 5 times in 10 years before they died. I'm not sure there was any conscious thought on their part, their certainly wasn't on mine.
I think they just accepted I was young and building my own life.
It happened with me, and I see it happening again with my parents and my siblings kids.
In my parents case there's actually a sense of relief because they want to do more travelling and what not while they're healthy.
It maybe there's something specific behind it in your situation, or maybe not?
D