Yeah we did have it solved for a long time. We had no screwworms at all in the country. That was a great solution that lasted decades. Why would having to do all the work of applying medication, paying for the medication, animals that you catch late dying of infection and paying for those animals, people occasionally getting screwworms, pets dying to screwworms, etc etc etc be better or cheaper?

Also they don't genetically modify flies they still just irradiate the larva.