symmetric encryption of '[stdin]' failed

[Fourhundred Thecat]

Hello,

I am trying to pipe output of tar command to gpg, and encrypt symmetrically:

   tar --zstd -cf - zz/ | gpg -c -o /tmp/zz.tar.zstd.gpg

this fails with following errors:

   gpg: problem with the agent: Inappropriate ioctl for device
   gpg: error creating passphrase: Operation cancelled
   gpg: symmetric encryption of '[stdin]' failed: Operation cancelled

The same command works when I change symmetric to public key encryption:

   tar --zstd -cf - zz/ | gpg -e -o /tmp/zz.tar.zstd.gpg

Why does gpg-agent interject itself into symmetric encryption at all?
What role does it want to play? Does it want to remember the passphrase?

Anyways, how can I encrypt with symmetric when input comes from pipe?

thank you,