The reason it doesn't get used as much is because it doesn't provide any benefits over GPG. GPG is actually more widespread and there is support in all email clients for it. With bitcoin only electrum supports it ATM.
Signing messages with addresses other than p2pkh ones is also not widely supported. So the authentication part is missing.
I'm not sure if ECDSA can be used to encrypt, I thought it was only possible to use it to sign with? (the DSA part breaks out as Digital Signature Algorithm)
Electrum uses something called ECIES. Only Electrum supports it though.