Why can't I expect them to add all 3 starters? They did it in Brawl, and Project M, for that matter. Besides, popularity =/= a good idea. (Just look at the Twilight movies.)
They did, for one character whose gimmick was cycling between those 3. This time is only one character though. Besides, you can't compare that between Twlight. That's just a bad analogy. You can't assume that because something is popular it means it's insta bad. Sure, there are terrible stuff out there that is unexplicably popular but you can't use that argument works in every scenario.
Lucario: Relatively speedy, charge up B neutral, martial artist, thin, humanoid. ZSS: Speedy, agile, charge up B neutral, thin, humanoid. Sheik: Speaks for herself. Mewtwo: Light, thin, humanoid, charge up B neutral. Are you starting to see the pattern here? And those are just off the top of my head. Smash is saturated with this character type. Chestnaut could theoretically offer a playstyle built around being big and moderately heavy, but also sturdy and good at counterattacking and blocking projectiles. We don't have a character archetype quite like that yet.
Those characters have very few similarities between them save for a humanoid figure. Again, that point is really invalid and those "patterns" are just stuff you are making out of nowhere. They play nothing alike nor look identical enough. If the character brings a unique playstyle (which Greninja does) it is a welcome addition.
Why wasn't Blaziken added back in Brawl, despite fan demand and crazy popularity? It wasn't recent enough to be marketable. Greninja is in this to be an advertising push. You admit it yourself below. Some of us happen to care about artistic integrity.
Blaziken had the bad fortune of being in a generation that came and went between Melee and Brawl; he wasn't in the spotlight any longer to warrant him a spot in the roster.
Artistic integrity? Man, I'm sorry but people who tend to say this like to pretend that they are "holier than thou" because they decided to like what others generally don't. Greninja is popular enough in the pokemon community that he is the 7th most used pokemon in online battles, so he is a well liked character. You can't honestly call some off people because they have advertisement; and compared to Lucario, Greninja has had very little, in a gen where the highlight were the Mega Evolutions. Imagine how this would go,
"Hey, what if we add one of the Kalos starters, I've heard that Greninja guy is pretty popular in the pokemon community"
"Yeah, but you know what, let's add Chesnaught. The guy is the underdog of the three which makes him an instant better choice than the cool ninja frog everyone has been talking about"
I'm also afraid that the dev team couldn't give a damn about your "artistic integrity", they are not looking to get creds with you and add the character that you prefer because it is being overshadowed by others. They are going to make the decision to add the one that will make a less amount of people mad, sorf of speaking. Don't let that stop you from keep telling that lie to yourself and believe that you are better than others.
Mewtwo was cut from Brawl, it looks like the non-overhyped (Yeah, I said it. You wanna make something of it?) Kanto starters have been cut from 4, Jigglypuff remains in despite lack of popularity. How can you tell me with a straight face that Pokemon doesn't have roster issues?
Between the pokemon games, those guys except for Jiggs are still pretty popular, so that remains consistent. Also, Mewtwo was planned for Brawl. Point still stands.
So basically, you're saying that Smash should be a popularity contest, and only fan-favorites should get in? Then what the flying fish are Wii Fit Trainer, Mr. Game And Watch and ROB doing here? Why was Fire Emblem included in Melee despite being a Japanese niche series at best at the time? Why is Ridley still not playable?
Never said that, so moving on to pokemon.
And when it comes to pokemon characters may I remind you that there are over 700 poke out there. They are mostly going to choose whoever is big in the media over your favorite, obscure and overshadowed pokemon.
There are several series that I only got into enjoying due to Smash highlighting them when I wouldn't have given them a second glance otherwise. Smash is a place for all Nintendo All Stars to shine, and constant fan-pandering just leads to rehashing the same ideas over and over again.
You call it fan-pandering but tell me, out of gen 6 who would you have chosen? Chesnaught, right? You want them to pander to you specifically which is why you try to make the whole Greninja deal look as dirty as possible.
Rehashing the same ideas? If we are talking about the character's moveset, we've stated how unique he is seen in comparison to the others, so that point is pretty much false.
It's high time that you've learned that the world doesn't revolve around you; just because you prefer others toward him doesn't make him undeserved or less well-liked. It's pointless to throw accusations of "selling out" or wasting moveset potential. Call it whatever you want, but the decision to include him was the smartest in the long run.
Let me explain in terms that will most likely be dying to use: not taking advantage of Greninja's importance in the pokemon media or "not trying to milk it" in order to add someone obscure that the cool, self-righteous crowd with "artistic integrity" want, THAT would have been really stupid.