It's extremely limiting and would make for an incredibly boring roster. I mean, those are the characters a majority of fans want, not every fan. Using myself as an example, Chrom is the only character I cared about from the newcomers.
A roster made from what fans want would've never seen the likes of Mr. Game and Watch, Wii Fit Trainer, Greninja, retro characters, etc. (Simon wasn't a popular pick before verg)
I'd rather have a healthy mix of popular and interesting characters than a bunch of crowd-pleasers that don't really bring anything new to the roster. Inklings have the ink stuff, Simon has the longest range, but Ridley and K.rool? They're fine representations of their characters, but they're very straightforward.
Smash should never focus solely on what we want at the moment, but also to whatever they have stored for us in the future and the many hidden gems through their history.