For example, any Administrator on the website can access your profile. In that, we can see your email address.
I can take that email address, google all or any part of it (which for most people is fairly unique) and find instagram accounts, twitter, old dating profiles, facebook, your employment, the list goes on. Most social media apps these days have a function that allows you to find users based on their email address.
We can go one further and cross reference with everything you've ever posted. You mentioned a favourite taco joint, or a school you went to, or your home town? We can check that against your time-zone (and let's be honest, most of you chose your local time zone didn't you? You'd be surprised at how easily that narrows your location down). Hell, there's even a field for date of birth on here.
Up next, we can pull your IP address, which is saved with every post you make, over the 10+ years some users have been posting here. Did you remember to use your VPN every time? I mean, every single time? Because I can download
public lists of VPNs and
TOR exit nodes, compare them to every IP you've posted from, pull out the ones that don't come up as public proxies, and check if there's a pattern. Maybe it's always the same exit node, maybe it's always a VPN from the same country, maybe you forgot just that one time and posted from your mobile device.