Defense contracting doesn't have an aversion to LLMs so much as it doesn't like doing anything that threatens the status quo. Many places sit comfortably 5-10 years behind the median of the rest of the industry or are stuck on proprietary tech stacks for arbitrary reasons.

I would rather deal with Claude refusing to follow instructions than be forced to write software in a proprietary framework that's been effectively EoL'd by its vendor then use Citrix to deploy software to a Windows box after a month long round of manual testing. The former is slightly annoying whereas the latter is a dire threat to your professional mobility and dignity. Your mileage may vary.