Parties and campaigns already buy & maintain huge private databases on this stuff. They wouldn't hesitate to buy slightly more to have that info, because gerrym

Parties and campaigns already buy & maintain huge private databases on this stuff. They wouldn't hesitate to buy slightly more to have that info, because gerrymandering is so powerful. Watchdogs and groups trying to fight gerrymandering (racially-tilted or otherwise) usually don't have as many resources. It's harder for the public to keep an eye on this without public data, while keeping it private-only barely inconveniences the most relevant bad actors.