“If everyone could see it”
Proceeds to show an alternate future where having seen it is apparently a status symbol, which implies that not everyone is able to see it
I guess the artist just wanted to make a “haha rich people bad” joke, but surely there are other ways to make the same joke without completely ignoring the hypothetical scenario you described literally one panel before?
Literally the beginning of the movie shows that Joy was there alone before Sadness showed up.