Possibly speed? Symmetric crypto is fast, and is often hardware accelerated. Asymetric is slow and not accelerated. Not as big an issue with ECC, but RSA als

Possibly speed? Symmetric crypto is fast, and is often hardware accelerated. Asymetric is slow and not accelerated. Not as big an issue with ECC, but RSA also has much larger block sizes, increasing the size of small payloads. It's been my experience that Asymmetric is used for kex (key exchange) or key agreement or signing, but encryption is done using a symmetric algorithm.