That's exactly my thoughts as well, the thing people who are alright with Finn being left alone is >He's just 17 you don't find your true love that young, he has time
Okay, but we don't see what happens after so it doesn't matter. Finn could get married to 50 girls at once, or he could've tripped on a stick and drowned on the beach after seeing the humans coming- anything could've happened thus nothing really happened.
If HW was set up more than not at all then he would've ended it with something and this still completely works in the vein of "the adventure goes on" the finale jerked off so much to. Finn could stay with HW for the rest of his life, they could've had a few years together and amicably broke up after, Finn could've had another retarded wet dream that destroyed their relationship, anything could've happened but not leaving him on a note like that feels like its disdain coming from the writers or something especially when everyone else except Simon ended up happy with a partner (and even then Simon at least had moment with Betty before she Golb'd).
People seem to only like it because they want Finn to be alone. There seems to be a thing against Finn having anyone, like that one video that pissed people off which was "Finn's single (and that's okay)" and shit. I feel like it's a mix of people not wanting to endure anymore romance bullshit like FP back in the day and maybe others who genuinely believe the /co/ shitposting about "cis white males shouldn't get happy endings" and crap.