EC ElGamal versus static+ephemeral ECDH
ElGamal appears to be used instead of Diffie-Hellman (or IES) in OpenPGP mostly because when that format was put together, there were some unresolved intellectual property issues surrounding both RSA and Diffie-Hellman, while ElGamal was unproblematic. This trend for ElGamal seems to stick around, mostly by force of habit, e.g. when switching to elliptic-curve variants.

If you look at ElGamal closely, you will see that it is, in fact, a Diffie-Hellman key exchange, where the resulting key is used to encrypt a message in a kind of one-time-pad system (the $y^r$ value is the DH output, and is combined, using the group operation, with the message to encrypt). Using the group operation allows for homomorphism, but when that property is not needed, it is a useless complication and overhead.