Folks can justify a purchase decision however they see fit.
When resell is worth more on the "back end" that's only because you paid more on the "front end". You only recoup a percentage of that front end premium if you're lucky. Heck yes a gasser is going to be worth less on the back end because it was worth less on the front end. A diesel is not gaining anything at all, its not appreciating. People tend to believe forum bull if that's what makes them happy
Having and having had more than a few diesel trucks expecting some type of windfall at resell or trade had nothing to do with the decision to buy them.