For a lot of people it's that those designs pander to their nostalgia
That's about it
I'm as confused as you are as to why Pokemon is such a rose-tinted glasses magnet, when so many other franchises commonly played back when the current general Internet userbase was younger are not. Or at least nowhere near to the extent Pokemon is.
I think the main reason is people dont like to associate pokemon with something that we eat. When desighns as blatant as ice cream and cotton candy exist, it rubs some people the wrong way and they tend to hate on them because of it. I personaly dont care, and those two i mentioned are actually quite cute and do have pretty good desighns to be classified as pokemon and not what there based on.