Because for projects like QEMU, current AI models can actually do mind-boggling stuff. You can give it a PDF describing an instruction set, and it will generate you wrapper classes for emulating particular instructions. Then you can give it one class like this and a few paragraphs from the datasheet, and it will spit out unit tests checking that your class works as the CPU vendor describes.
Like, you can get from 0% to 100% test coverage several orders of magnitude faster than doing it by hand. Or refactoring, where you want to add support for a particular memory virtualization trick, and you need to update 100 instruction classes based on straight-forward, but not 100% formal rule. A human developer would be pulling their hairs out, while an LLM will do it faster than you can get a coffee.