See I don't even think it's a matter of happiness vs. sadness. The Epilogues do have a lot of fucked up shit happening in them, that's undeniable, but they also both end in very very sappy sanctimonious ways- one with all the characters making their badass stand to hunt down Dirk and the other with the wounded but still stable characters either coming to terms with themselves/leaving to find out who they really wanna be. They do aim for very big FUCK YEAH moments and to some extent succeed?

I think there's a deeper issue here, one I am more inclined than not to link to many of Homestuck's other late game changes even though they impact different groups to different extents.

Homestuck is, uh, kinda small! It's small and kinda insular and the grandness and majesty it pushes out never really reach that epic amazing conclusion they seem primed to, because every time you get close to it the story pulls out the curtains to wind back that grandness back into the dumb incestuous samey tapestry that everything else is part of. I think even the basic fact that people wanted an Epilogues emerges from that kinda dissatisfaction with how small and brief Act 7's "happy ending" is from the amount of lollygagging and weird bullshit it takes to get there.

For "candy" minded folks that looks more like an Undertale True Pacifist type "you personally walk through and see how every person you helped along the way is better off for you having been in their lives", for "meat" minded folks that looks way more like Problem Sleuth's high octane "literally every single loaded chekhov's gun fires simultaneously and the ordinarily smarmy dweebish tone shifts as the anime music kicks in and PS punches the antispiral into another reality", most people are in the middle

but no side really likes the thought of the "endless weightless CW space serial meets Real Housewives Of Earth C" vibe the Epilogues end off on because that's not a climax it's not a resolution it's an endless anticlimax, no sweetness no umami just a bitter coffee you sip at a private taste testing in the world's most gentrified studio loft apartment. And to those ends I think it's just what climax is enough to get people off of homestuck.