It hurts Apple brand
If someone is selling exploding batteries that fit an iphone, it's up to the government to shut them down for being unsafe, or the burn victims to sue the exploding battery repair shops.
Despite their marketing, Apple is not the only company in the world that is capable of making a non-exploding battery.
The FUD about iphones being some magical object carried down on the wings of angels and suddenly becoming unclean and flammable because a third-party battery was inserted is ridiculous.
Laptops have had replaceable batteries for decades without the sky falling down - until the Apple reality-distortion field was successfully engaged to disable people's rational thinking.