The only consistent pattern i noticed is that its an obvious character that the speculation community somehow doesn't have on their radar. Last three characters at least were like that.
Honestly, that could be applied to all of Ultimate's DLC lineup. Even Piranha Plant.
: A lot of people were against Bandana Dee and called him "Hat Goomba." What makes you think those same people would humor a literal piranha plant getting in?
: Nintendo chose the DLC, and that somehow meant they would only pick characters to "shill" their games like Sylux and Poochy. Everyone was blindsided by Joker.
: Was leaked via the Brave datamine, but even then, there was some people who thought it could refer to a different Square character. The people in the Dragon Quest camp assumed we'd only get Erdrick. The Luminary as the default Hero, plus Erdrick, Four, and Eight tagging along threw everyone off.
: Someone speculation actually got right. But I guess there was that Banjo vs Steve war with the Grotesque Steve model.
: No one gave one iota to Terry until Nintendo ****ed up and accidentally leaked the SNK copyright.
: No one considered a Nintendo character because it went against the "Fighters Pass is all third-party" dogma. After listing off a bunch of third parties and being told no, people settled on Dante before getting angry at Byleth for "ruining" the hype.
: ARMS was deemed dead and buried because everyone assumed the first rep had to be Spring Man because he was "The Face of ARMS," but he got Assist Trophy'd. Some of them still insisted it had to be Spring Man, while Min Min was the fan favorite (and got in), ResetERA wanted Twintelle, and /v/ wanted Max Brass.
: A "meme pick" that wasn't taken seriously. Thought to be dead after Banjo got in first.
: Either people didn't think we'd get any more Square content because "they're stingy," people wanting a different FF protagonist, or Geno fans wanting Geno. All the Game Awards predictions saw the usual third parties with a hint of Jonsey sprinkled in.
: Those same third parties that have been circle-jerked to death with special guest Dr. Eggman.
"Pyra & Mythra? Rex is a Mii costume. It won't happen. Huh? Just Pyra & Mythra? Don't be ridiculous."
All talk for a Tekken rep was for either Heihachi and Jin. After Heihachi came back as a mii costume, Tekken was deemed unlikely to get a character because of the idea that "they wouldn't add a Tekken rep after the Heihachi mii costume. Why not just save the Heihachi mii for the Tekken reveal?" As for E3 itself, people were expecting a hype™ third party like Master Chief.