Pikachu is on the list, he's number 48. And no one was arguing that Scizor isn't one of the more popular Pokemon, but just because he ranks high with the demographic that voted on this poll doesn't mean he is in the same class as the Pokemon playable in Smash. Scizor really has nothing going for him other than above average popularity. Plus he's already been dismissed by Sakurai when a 2nd gen was actually a possibility.
Plus there are 16 other Pokemon above Scizor on that list (not counting Mewtwo or Charizard) and I'm sure some of them would be able to work in Smash, but just because they have popularity among a certain demographic doesn't mean most of them are comparable to the iconic series staples and mascots already playable.
Oh geez, for some reason I read he wasn't on it. Most of the Pokemon above Scizor are legendary, I'll do the same post for 18 up to Mewtwo.
Entei #18 Legendary Pokeball Pokemon
Gengar #17 (I would have no problem with this one.) But he floats and people could pass threw him.
Suicune #16 Legendary Pokeball Pokemon
Venusaur #15 We already have Ivysaur, this would be repetitive.
Ho-oh #14 Legendary Flying Pokeball Pokemon
Articuno #13 Legendary Flying Pokeball Pokemon
Arcanine #12 Ever since Ivysaur I don't see a problem here
Gyarados #11 Floats/Swims
Zekrom #10 In background, massive legendary pokemon
Tyranitar #9 No problem, he would just be very heavy
Zapdos #8 Flying Legendary Pokeball Pokemon
Rayquaza#7 Flying Legendary Boss Pokmeon
Mew #6 Floating Legendary Pokeball Pokemon (They could probably make Mew work, but we already have Mewtwo)
Dragonite #5 No problems from my side
Lugia #4 Flying Legendary Pokeball Pokemon
Blastoise #3 Already got squirtle
I see potential for a few, but most seems unfeasible, Still can't believe I managed to mis Pikachu on the list