4-5 years ago you could apply the 80/20 rule to those who owned 26" bikes. Now, some of those will have embraced 29er for specific reasons - like you did. But, what about those who had no need to buy a different wheels sized bike? The industry has basically said, "screw you, everything you invested in is worth sod all*"
This is different to an "I invested in the wrong thing" issue, no one made a silly decison buying a 26er they had no choice, so they've been pushed into a devalued market by the industry.
But then again, I guess not mtbs could be seen as an investment so is it fair to say they are effectively disposable?
*assuming you want to sell it.
Edit - a it late to respond.