Yes, it's costly to maintain the combinatorial interactions between configurations. But 'make it a setting' has further costs- when you're supporting a customer

Yes, it's costly to maintain the combinatorial interactions between configurations. But 'make it a setting' has further costs- when you're supporting a customer and you can't figure out the exact state they're in, when you can't make sweeping product changes because 8% of users have some incompatible option set, when someone implements a bad feature and there's no strong way to keep it out if you can just 'make it a setting', or when a feature becomes obsolete but is kept around 'as a setting'. It relieves the product team from one of their most important responsibilities.