Especially when the system's successor has no backwards compatibility. A few WiiU games will be ported to Switch, as it's already the case with BotW and MK8 (and it's almost guaranteed we'll get Smash Bros. too in the near future), but definitely not all. And for all its shortcomings, the WiiU had a small but excellent software library (that nobody should miss out on, imho). So it only makes sense to sell your old video game systems if one's the type to never replay any games. Also I don't think the few miserable bucks Gamestop and Co. offer are a fair deal for anyone but them.