Because diseases have a tendency to recombine and jump hosts - it could become a human plague- similar to malaria..
> This initiative introduces X-ray sterilized male mosquitoes in target areas as part of a Sterile Insect Technique (SIT) pilot program
It is highly unlikely that x-ray sterilized male mosquitos would cause a human plague similar to malaria.
The article has mosquitos "releasing toxic proteins in their semen". Seems like the sterilization is a much better option. "We promise it's not toxic to humans" didn't turn out so well for RoundUp.