I guess I was confused on why the seller would not counter offer/ask for the full price before moving on
You made a lower offer, someone else offered full price.
Since you made a lower offer, you are more likely to say "Let me think about it." The other guy was willing to buy at full price.
I suppose he could have offered to you at asking price first, but let's say you wanted to think it over a day, then decided that you didn't want to pay the asking price. Meanwhile, in that one day, the other guy found what he was looking for elsewhere. So when he PMs the other guy, he's no longer interested.
So it gets relisted. And it starts over again.
Here's a story for ya:
I got a modified Z28 gauge cluster for my 94 Caprice when the digital quit. Six months later, the transmission dies. Due to the cost of a remanufactured 4L60E (which wasn't much more than having mine rebuilt), and the condition of the car, I part it out.
The gauges got a lot of interest. They were SPF 5 ****ing times before I shipped them.
Five. And it was because "I'll offer this much if he doesn't get them." "Let me think about it." That turned into "Found them elsewhere." "Bought [this] instead." "Something came up, I dont have the money now."
If I was the seller, you made me a lower offer if the first deal fell though, and someone else offered me asking price if the first deal fell though, I woulda sold them to the other guy as well. That's an easy sale, vs a possible PITA that lasts a few months.