I found we mostly do it for five reasons in order of increasing likelihood:
1. They ask us to (Eden Belmont)
2. They're posing a risk to themselves/others and/or breaking the law (Chloe Sagal, Greta Gustava, etc) or are pedophiles/sex offenders (Nick Bate)
3. They're an insane idiot who believes they will literally die if exposed and/or lives in mortal fear of being murdered by people they've never heard of and will never meet (Jake Alley, Felisha)
4. They're actively trollshielding/supporting/aiding existing cancer-tier lolcows (Norasphere, TLL)
5. It's someone who will chimp the fuck out on a biblical scale just because their personal information is now available to people who will do fuck all with this information (Crystal Hall)
There's plenty of overlap, and there's many exceptions, but these are the most common reasons.