If you are just using AH you aren't encrypting your traffic so it isn't really comparable to wireguard or openvpn.

Or maybe you encrypt at another layer and just want strongswan for the interconnection without too much overhead.

Or maybe you do not care about the encryption, but care about the virtual and private part of VPN

There are many usecase. There is no one size fit all.

The question was if there was a reason to switch away from OpenVPN ;)