You forget that these people are
purposefully ignoring the truth at this point, which makes the whole thing funny because of the limits their delusion just doesn't seem to reach. He'd very much rather them being the joke instead of him.
Dream is still celebrating this "victory" where he can keep having underage fans on a leash thinking he's a cute skinny boi and this big bubble
will blow up eventually. He might show himself by accident, yearbook and more proof photos might possibly spread eventually or, as impossible as it sounds, he will really show himself for some event because not even he can run away from the truth forever (because he's so fat, he can't even run well

) and he just won't lose the necessary weight before that, unless he gets some serious surgery, diet and exercise ASAP.
I genuinely believe that he can make his brother show and those blind fangirls will eat it up, even if deep down they just know it's not him but won't ever admit it. If, after that point, they keep their strange mindset... well, that's a tragedy and they will know better, after years.