I don't think there's a general rule, but some individuals have their own rules. I think I send out about 50 cards every year. I do keep track of who sends me one back, but mainly out of curiosity; that alone doesn't affect my card list for next year. I receive maybe a dozen cards each year--everyone who sends me one is on my list, but obviously that's a lot of recipients who aren't
sending me cards. That's cool, some people just aren't into that.
People are added or cut from my list based on my overall relationship
with them. Old friends I literally haven't heard from, in any medium, in years? I feel comfortable cutting them from my list. On the other hand, I've added in more distant relatives (like Bob, my second cousin once removed) if we've reconnected in the past year. I heard that my uncle's ex-wife was asking
for a card from me, so hey! On the list she goes. Cousin who ignored me when I asked for his mailing address? Cut, because I don't want to force contact on people if they're telling me they don't want it.
I really enjoy sending the Christmas cards and want to keep it as a pleasant experience that gives me a moment for positive thoughts about each recipient. If they don't want to reciprocate with a card, that's fine, though it would be nice to hear from them in some other way once the card makes them think of me. So, maybe think about that, if you're wondering about reciprocity--they might enjoy a brief "how've you been" email inspired by their card.