POS? No. It was one of the more unusual designs for vehicles (and in its time period, it was hardly alone in THAT aspect, but it worked better than most), but I think one factor was that it had a lot of moving parts, and as cited, perhaps easily lost ones. I'm not even sure my own is entirely intact, and all it's ever really done is been parked in a room or a closet for its entire existence.
Additionally, while I have no production statistics, the General was the first vehicle in several years, really since the Flagg/Terror-Drome/Defiant days, to do a vehicle of rather considerable size, and at a time when such items were pretty unusual for any toy line. It might have had fairly low production numbers, relatively speaking.