Eh in our family none of us kids did that it just wasn't a family norm. Certainly wouldn’t have been a deciding factor for when to stop.
Tit for tat wasn't really a thing in our family like my cousin never sent my mom a birthday card in the mail much less a gift but it's not like my mom said "welp too bad so sad you get nadda from me", same for Christmas gifts.
Whatever family norms are should be what the OP is working with.
It’s not about tit for tat. It’s when the scales of gift-giving have been one-sided for years and years, there comes a time when you ask yourself the question the OP is asking.
Given that the OP is talking
grand nieces and nephews, that translates to probably thirty or more years of gift giving for nieces and nephews before that. That’s a LOT of gift giving over time, and it’s not always easy. (For instance, I had to send packages out of state for 20 yrs. Before
Amazon. So shop, wrap, go to post office and send, etc. Twice a year, at least.)
I realized when asking myself the same question that the people I’m closest with send me a birthday greeting, too. I’m not talking gifts, or even sending a card - I’m talking shooting a text. If that doesn’t happen, then I just don’t see that it’s something that one is obligated to keep doing forever and ever. I mean, sure, if one sees these people and wants to give them something, then hey. But if not, and especially when it requires going out of one’s way to get and deliver gifts, especially as one gets older, then I think it makes sense to end the ritual.
It doesn’t mean if one sees them, they can’t give them gifts then. If that makes sense.