Most likely theory, IMO: people preordered Zelda for the discount (BB and AMZN offer like 20 percent off MSRP), expecting to nab a Switch later, but later hasn't yet arrived. Based on ebay sales rates, maybe soonish.
Yes .. the early discounts on games explains it. Very odd from the typical way discounting happens on XBox, etc. Typical games lose value a month or two after release. Nintendo crap either stays the same, or goes up in value because of lack of availability.
two points of anecdotal evidence: i bought a special edition to preserve and a retail version that i'm playing. my brother-in-law bought a switch retail version but is playing a wii u digital download.