The thing about the Speedmaster Professional Moonwatch is that it’s so easy to buy and to sell. It’s an extremely ‘liquid’, marketable watch and can be had for a reasonable price. Hence people often sell or trade them when they’re temped by another watch. Usually though, they wind up missing it and buying it again, sometimes repeating the whole process several times.
If it were a more expensive or rarer watch this might not happen and you might see a lot fewer of them on the second hand market. That said, the Sub is a much more expensive watch but it’s pretty ubiquitous on the second hand market too. Somewhat similar dynamic in that it’s an easy watch to sell.
Sometimes it takes several tries until you find the Speedy that really sings to you. I’m on my third one - a 145.022 on a 1450 bracelet - and this one should be a keeper.