Says who? We just got the best selling game of all time added as DLC and the villain from the best selling jrpg of all time as DLC. And sales are the reason we always get pokemon Soooo
Which has nothing to do with Smash requests either. He's the biggest JRPG character on his own merits, not cause of "FFVII sales".
Sales are not why we get Pokemon, lol. Pokemon in itself is one of the most recognizable franchises and comes with constantly unique and interesting characters, making it very easy for Sakurai to look at for a potential newcomer. He sets aside a spot for them sometimes(like twice). Most of the Pokemon were in because of the character being iconic, a cool concept, the anime, or because he knows it's coming out soon and they'll be easy for people to know who they are. The pokemon themselves help sell Smash, sure. But that's a natural advertising effect. Pokemon sales themselves aren't a core factor. There's way more than that. Sakurai, for that matter, wouldn't have chose Greninja and Incineroar if he didn't have moveset ideas for them. That's another key factor of why they actually got in.
Let's actually look at them;
Pikachu - The freaking mascot and from a hit anime
Jigglypuff - Super popular in the anime and an easy clone type character
Mewtwo - Super iconic, and coming off from a hot new movie, and also had a clearly easy moveset idea to work with(which would've taken too long for Smash 64)
Pichu - The mascot of Baby Pokemon and also highly popular
Lucario - New Pokemon way before "sales" would've made it clear how popular they were. Based heavily on the anime itself for the moveset, and that took a year to make.
Pokemon Trainer - A concept that represents actual Pokemon training, by using a generic Trainer with three of the top most popular Pokemon, the starters.
Greninja - Chosen before sales could be taken into account. He had no idea he'd be super popular either.
Incineroar - Literally got in over Decidueye due to the Wrestling motif
Sales at most could be contributed partially for the last two, but that only gives him a reason to set it aside, not to actually who is chosen.
Never mind, again, Sales =/= Smash Requests. They're only slightly related.