I do think a lot of people don't fully "plan out" their build. I think they get a spark of an idea and think it will be the best thing but when it comes time to build they decide against it and try to not only get their money back but also fund another purchase....could be wrong but that is what I assume is happening a lot of times.
The thing with Warmoth is that they are high quality but still not as recognized nor valued second-hand as Fender MIA. Also, Fender MIA, MIM, MIC, etc. typically have standards that are the same and identifiable by the serial number. Warmoth's second hand could be ANYTHING....from wood selection to neck shape to fretboard radius to size of frets to inlay material to body routing to body specs etc. Alot of time with Warmoth, your custom "ideal specs" are not ideal on the second hand market.
Just my $0.02.