Time to bring up MvC yet again.
The reason we got Marvel vs. Capcom 3 was because sales of 2 (the series' Everyone Is Here, nonetheless) on Xbox Live proved that MvC still had over a million fans. 3's roster still focused on using new resources to make new fighters, rather than just continuing to reuse the same dated sprites* so fans didn't have to worry about Mega Man being removed. This resulted in a smaller roster overall, but people mostly just cared about getting more MvC.
*This is more of an "ew Morrigan's sprites" thing than "ew sprites"
I'm pretty sure the other reason was that Capcom had a team capable of making Marvel vs Capcom 3. The team that created Tatsunoko vs Capcom, which was a success. And Marvel vs Capcom 3 followed up on a bunch of gameplay elements of what Tatsunoko vs Capcom did, like the 3 Attack Buttons and 1 Partner Button, X-Factor being an follow-up to the Baroque system, etc. Also quite a bunch of characters like Viewtiful Joe, Zero and Frank West first appeared in TvC, and not only did they come back for MvC3, but also concepts that didn't make TvC, like Phoenix Wright and the Ghosts'n Goblins stage.
Like that is another factor to why Marvel vs Capcom 3 happened. Not just the fact that Marvel vs Capcom was still popular with MvC2, but because they had an established team that made Tatsunoko vs Capcom, which was a good game and had Western demand.
I wouldn’t say we’ve become accustomed to not losing characters. It’s more so that now that everyone is back after 20 years (since Melee) it just be a damn shame to lose them. Just like it was a damn shame to lose Cyclops, Juggernaut, Classic Mega Man, etc. in the move to MvC3. Once you get a taste of everyone is here it’s hard to warrant wanting to go back without feeling like you lost something.
To this day MvC2 is STILL substantially more popular than MvC3 and that’s likely to do with the abundance of characters and how MvC3 cut a vast amount of popular characters. Im willing to bet that in the future if the next game does cut a large amount of characters, Ultimate will remain one of the more popular titles alongside Melee. You cut a character and you have a possibility of losing their fans as customers. It’s just how it is.
As a Snake fan I was actually relatively close to skipping over Smash 4. If it hadn’t been for some solid choices like Mega Man and Little Mac I likely would have skipped on it. One of the versions at the very least.
It was really just Mega Man that had the outcry. Other notable characters like Strider Hiryu and Venom had nowhere near as much an outcry.
And how many popular characters did MvC3 really cut from MvC2? Cause aside from Mega Man and Strider Hiryu, I don't think anybody else really cared about any other Capcom characters in MvC2 at the time. Nobody certainly made a deal about characters like Captain Commando, Jin Saotome, Hayato, Ruby Heart, Amingo, SonSon and certainly not the abundance of Street Fighter characters. And for the Marvel side, the only notable ones I can remember people talking about a bit were Venom, Juggarnaut, Cyclops, Cable and maybe Thanos.
That said, even when we lost those characters(with only Strider returning for UMvC3), we got so many more popular characters in return. For Capcom, we got 3 Devil May Cry characters, 4 Resident Evil characters, Mike Hagger, Arthur, Phoenix Wright, Amaterasu, as well as the MvC appearances of Viewtiful Joe, Zero and Frank West, and for the Marvel side, we got Thor, She-Hulk, Ghost Rider, Hawkeye, Deadpool, and certainly characters who have gotten alot more popular lately, like Doctor Strange, Dormammu and Rocket Raccoon.
I don't think there is much of a popularity difference between MvC2 and MvC3. And the dedicated Character Mods for Marvel vs Capcom 3 that have been getting alot of attention, like Cyclops, Psylocke, Monster Hunter, M. Bison, Rashid, etc, certainly have been helping MvC3's popularity. But I'm not denying MvC2's popularity and I'm certainly not against Marvel vs Capcom 2 getting a re-release.
But something about saying MvC2 is more popular because of the characters feels very off to me when Marvel vs Capcom 3 brought in alot of new popular characters in turn and nobody made a big deal about characters who didn't return, aside from MegaMan. Or maybe it could be because I'm more a Capcom fan than a Marvel fan and the MvC3's Capcom side looks better(in most aspects) than MvC2's Capcom side aside from not having Mega Man.