[swarmee]

I try to respond ASAP as well, but here are some possible reasons that people ghost you once you've made a counteroffer:
1) They're still considering accepting your offer, but decided to put other offers out to sellers of the same card to see if they can beat your price.
2) They're still considering accepting your offer, but have to move money into PayPal or sell something to be able to afford the new price.
3) By allowing the offer to expire, they're showing you (in a passive-aggressive manner) that they don't need the card. So if they come along three days after your counteroffer, they may offer their original price again because you haven't sold the card in the meantime. < "Game theory" theory
4) They are on a cruise and cannot access the internet to see that you counteroffered.
5) They would rather let the counter expire than reject it, and consider angering you. Some people are that timid, and many sellers on eBay will get agitated over flat rejections.
6) They don't care that much. There's no requirement for you to sell it to them, because you have the ability to sell it to anyone else while their offer is outstanding. So there's no harm to you in letting it expire.
7) Ghosting is now a part of culture. Shy people have decided it is better to disappear than to be involved in things they're tired of.