To be fair, Isaac's fanbase was setting themselves up for major disappointment by not reigning in their expectation. The Grinch leak by itself would've made things bad, but on top of that, we got that mystery item, the September Direct theory, and the picture which was 100% hinting at Golden Sun and a playable Isaac because of the angle the picture was taken.
Sakurai can't disconfirm every popular character at once. He was probably trying to save Isaac as a notable reveal so his supporters would be surprised that his AT was back, but just like we do with everything, we looked at nonexistent cues, jumped the gun, and told ourselves that Isaac was playable.
I've said it countless times, but even with all the evidence that Dark Samus might be a playable character after the game was revealed at E3, I maintained that it wasn't confirmed, just that the possibility went from "Never going to happen" to "It might happen." Because I knew how much of a long shot it was even with the evidence, so I left a lot of room for doubt.
And when the Grinch hoax happened, I was surprised at how many people jumped on the "It's confirmed, it's legit" train so quickly, despite all the reasons to question its validity. It couldn't necessarily be disproven, so there was room for hope, but I heavily doubted it based on a number of issues (I laid out a whole friggin' essay about it the night before the Direct). It sucks that so many people got burned by it, which is exactly what the creator wanted to happen, but hopefully that incident will serve as a reminder from here-on-out for people to temper their expectations, so that this kind of thing won't happen again. Hopefully.
Here's the thing about fandom: obsession doesn't have to be negative. A fan being attached isn't a problem; a fan being attached and being a ****ty person is a problem.
Anyone who talks with me regularly knows there are games/characters I love and will talk someone's ear off about if one lets me. But I'm not going to be ****ty about it blowing up someone's Twitter or fighting with someone over the merit or inclusion of my favorite things.
It's not that hard.
You're right, it really isn't that hard.
I've been playing Smash since 2002, and I've never had a character that I really loved be in any Smash game until now. I ended up growing attached to R.O.B., and he was my favorite Smash character for the duration of Brawl and Smash 4, but he wasn't a character that was shown off before Brawl where I went "YES! FINALLY!" or that I had much of a personal history or attachment to, outside of Mario Kart DS (though I do own an actual R.O.B. and Gyromite accessories, which I've played a handful of times over the years, but I can't remember if I got it before or after Brawl).
When Smash 4 came and went, and I didn't get any new characters I liked, I was still excited for them because they made other people happy. Seeing Maximilian and others lose their minds over Cloud and Bayonetta made their inclusions worth it. I like seeing other people's wishes come true, even if it means not all of mine will. When Daisy was announced, I didn't personally care, but I was still excited because I knew that it was a big deal for a lot of other people, so I thought it was awesome. I've never played or cared about Donkey Kong, but I knew K. Rool was a titan in terms of popularity for Smash, so I was hoping he'd get announced, too, if only for everyone else.
Part of that is just recognition of "Beggars can't be choosers." My top two are Dark Samus and Chibi-Robo. Both had little chance of anything. So if neither of them were confirmed, I could just go "Yeah, all right, whatever," because I'm not going to say "This character with little popularity, relevancy, or significance
deserves to be in the game damn it, and if they don't get in over Incineroar, I'm not going to buy the game, and Sakurai's a ho." The only case that could've been made for either of them was that, since Ridley was said to not be viable, Dark Samus is the next in line for a Metroid character with plenty of potential and less issues, and Chibi-Robo had a 3DS game in 2015 that gave him a bit more relevancy and moveset potential, but that's it. I wasn't going to pretend that either of them were any more important than they actually were.
Somehow... I got Dark Samus, and Chibi-Robo as a Mii costume. I can't tell you how that happened. I voted for Dark Samus in the ballot, but I didn't think it would
work. I guess those 16 years of patience paid off, or something. Even if neither of them are full newcomers and compromises had to be made to include them, the fact that either of them made it in at all is huge. Some people complain that Dark Samus should've been a full character, but it was this or nothing. Echo Fighters are a sign that "We can't justify this character as a full newcomer, but we can at least get them in the game this way," which I can't necessarily disagree with.