Why is it difficult to encrypt large amounts of information using quantum key distribution?
I believe the end goal is to use the QKD data as a one-time pad, so the QKD rate would need to be the same as the plaintext data rate.  That is the only guaranteed-secure method.  (Although I think QKD might be a bit of a scam.)

Also, you can't use a key forever.  I recently made a 400Gbps AES-GCM encryptor.  You're not supposed to send more than 2^32 blocks with the same key, because it starts to get easy to forge tags after that.  This corresponds to ~8 hours' worth of data.