Yeah, same. I remember the reactions to the Direct were basically "lol suck it Shovel Knight fans" while SK fans were like "it's him! he got in smash!"
I think it's due to how this community perceives "worthness" in that, for example, Isaac fans got less than they "deserved".
To be frank, Isaac and Shovel Knight are two different stories for why fans feel very different.
The reason why it was an honor for Shovel Knight, their devs, and fans, is because Shovel Knight was very new at the time of the ballot and was also apart of the Indie genre. The fact that Shovel Knight's went from these humble begins, to getting noticed by Sakurai and get a mobile model in one of videogame's biggest crossover is astonishing and a milestone for alot of people and the industry, probably alot more than most people realize.
Isaac however, had a big support base that goes much farther back spanning since
pre-Brawl with some people supporting Isaac for more than
a decade, already has been an assist trophy, and had a heavy hitter title that created two sequels on what was meant to be the beginning of a new series (since there was a cliffhanger and some loose ends, there was probably supposed to be a 4th game). When Smash 4 came around and Isaac was no longer an assist, many people saw this as Isaac's chance to be playable. This increased during the Ballot, where Isaac's presence became as a dominant as ever and it finally be the time to show how many people would be fine with Isaac being a newcomer. This essentially "worsened" when there was also a big leak and some insiders claiming that Isaac was playable. "Could this be the time Isaac can finally be playable?" but Isaac was shown as an AT at the wrong time, and thus it spawned the largest amount of frusturations.
It's liked comparing apples to oranges. On one hand, for Shovel Knight's first time in the spotlight, his support did really well for him to be an AT, and it was milestone for Yacht Club. On the other, this was Isaac's third attempt to be playable with many people who've been supporting Isaac for years, only for that support to be crushing back down at the last/worst moment to being back in the same role from Brawl...
you decide how well that would've went.