If I wanted to find someone in my city, a global website would be the last place I'd look. Maybe the people who use a global matching platform are more interested in finding someone with specific skills / interests rather than someone who lives nearby.
Maybe there's a misunderstanding because there are no obvious screen shots but it says you can filter on location. Thus, a "global" matching platform becomes a local one. It's not is if one is endlessly scrolling 15000 profiles hoping for a local person to appear.
It's still a relative numbers game. Finding a nearby potential co-founder in a subset on a popular website such as YC is more likely than a local website such as lasvegas.craigslist.org
I would assume that a cofounder matching platform with 16000 profiles has a similar problem, it's just too few people to bother looking for local matches.