Mickey and the gang are ubiquitous on all kinds of merch, but I think what hurts his recognition might be the various ways he's presented?
Mario is just Mario. There aren't a ton of
versions of Mario. Yes, he's been updated over time, but once his image changes, it seems to stick for a while.
Mickey on the other hand appears as a mascot, as the "classic" version that you see on wristwatches, in the new-fangled way with the new animated series, and a ton of other ways, and many of these are appearing in the parks, on
Disney+, and merchandise, etc simultaneously. I don't know if that affects how people perceive him as Mickey Mouse, or if they see another version and say "that looks like Mickey Mouse, but not the one I'm familiar with"
Idk, I'm just spitballin'!