Some great games at excellent prices are sitting for a long time. Resale market is down. LCD and remake era effect? Market saturation? Also remember, your mods are YOUR mods. People may not want to pay for them because they have a different vision despite it being a beautiful game or the mods push buyers beyond their comfort zone on price. Although I’ve never modded games over the top, I’ve been pulling back because I’m tired of taking a “mod” hit.
I think people are becoming concerned about dropping the coin for a game like this and taking a loss at sale time.