Because this isn’t simple law. It feels like simple infringement, but there’s no actual copying going on. You can’t open up the database and find a given duplicate of a work. Instead you have some abstraction of what it takes to get to a given work.
Also it’s important to point out that nothing in the law is sure. A good lawyer, a sympathetic judge, a bored/interested/contrarian juror, etc can render “settled law” unsettled in an instant. The law is not a set of board game rules.