Just to play devil's advocate, couldn't sending zero-day exploits to a foreign nation's intelligence service potentially cause the sender significantly more trouble.
The other angle is that you are obviously doing it in good faith, on the assumption that they will try to work with the vendor to fix and responsibly disclose the vulnerability
"Israel reached out to US hackers for ‘Zero Days’ tools" - https://www.timesofisrael.com/israel-reached-out-to-us-hacke...
Why?
For example, the Internet giving every crackpot wingnut on Earth an equal voice with scientists is how we end up with measles outbreaks.