This is likely putting too much faith in the Crunchbase data.
In my experience, Crunchbase very frequently leaves out some founders. Often, only the most prominent founder will be reported, thus underreporting the instances of having 2+ founders.
But then again how many of these companies with cofounders, really only had cofounders-in-name-only? Where one person really drove everything but at some point thought - oh shit, if I'm going to be successful, I need a cofounder!
Given the dogmatic advice "YOU NEED A COFOUNDER", I'm sure a lot of it's title inflation - what would normally be first employees are elevated to founder status to look good for the pitch deck or just to follow the advice. That said, they're still going to be quality people - less met at a find-a-technical-cofounder event, more Biz Stone style "can my title be cofounder lol?"
Probably the vast majority of startups have a dominant cofounder. You might call them cofounders-in-name-only, but that still validates the notion that you're better off finding a cofounder (even if they're not as central).
In my experience, Crunchbase very frequently leaves out some founders. Often, only the most prominent founder will be reported, thus underreporting the instances of having 2+ founders.