Can I ask why? What is so dangerous with asymmetric crypto compared to symmetric crypto?
Another big reason is that public-key algorithms are parameterized to an extent symmetric systems aren't. Two random numbers is all you need to safely encrypt something with AES. Diffie Hellman, the simplest of the public key algorithms, needs a prime, a generator, and random private keys with particular relationships to those parameters.
Even though it's theoretical, the side effects of this fact surface from time to time as engineering issues in asymmetric crypto: all information that the attacker might need to break asymmetric crypto is more or less in the ciphertext, intuitively suggesting it's easier for asymmetric crypto to catastrophically go wrong.
It's great that one-time pad exists, but it's not really relevant in actual crypto code, right?
The only actual reason I can think of is that symmetric crypto is easier to write and understand - you just mangle and xor some text back and forth, while in asymmetric crypto, you need to understand fairly complex algebra. But again, that's not that important if you use existing primitives, right?
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.