I have to say this is nothing new, I myself was told this by my daughter after her first child, we were a tad hurt, but then on thinking about it, if it's the first they want to bond, set about getting things in order, nurse comes in for 10 days after homecoming, their learning, I remember my MIL, would just arrive no phone call & she had to get 2 buses to get to us.
Everyone's different, after my daughter realised the work involved, we were there every day.
When next baby was due we stayed a few days before & a good week after.
Remember, new parents emotions are all over the place, when they see you they want to appear confident with baby, you see grandparents have done it before, hence they want that feeling of "look we can do this".
I just think go with the flow.