Linus shared the candy Lucy requested for him during trick or treating with Sally
Considering how much Sally was yowling about being owed restitution on Halloween night, doing that would be the obvious thing to do for Sally. Of course, he'll regret it, considering Sally would take that gesture as proof he's her "Sweet Baboo." A big chunk of the folks handing out treats are resentful Jerkass dudebro teenagers
The parents deemed them too old or Trick or Treating (and would spend Trick or Treating with edgier Halloween pastimes like trashing property with toilet paper or raw eggs, kicking and smashing jack o' lanterns, and writing obscene messages on windows with bars of soap), so these young edgelords thought it would be a "real scream" to troll the "known Butt-Monkey" of the children by handing him rocks. The rock-giving adults are probably a lot fewer in numbers, and the rest just want to relax or went to local adult-oriented Halloween functions of their own. The rest can be explained away as "absurdist humor". Charlie and Sally got compensated for the rocks and pumpkin patch fiascos
Violet's parents knew about it and let Charlie take home a bunch of leftover candy and treats for himself and Sally (and likely gave the neighbors a good "Reason You Suck" Speech ). The Great Pumpkin came while Linus was asleep.
In a twist, The Great Pumpkin is real, Linus just didn't get to see him because he came after Linus fell asleep. The Great Pumpkin was the one that Lucy carved up in the beginning.
That's why it never showed: Lucy turned it into their Jack-o-lantern! Linus even cried that they killed it.