Full explanation:
Most users of UH VPN utilise it for remote access to their corporate or home networks. This often requires the use of concepts like split routing where only certain subnets are routed over the VPN. OpenVPN achieves this much more easily using it's "push" directives wheras a solution involving wireguard is much more complex.
In addition to this, UH VPN is in part a VPN authentication system as a service, as such it requires a VPN protocol capable of working with a custom authentication system. OpenVPN does this very nicely using its "auth-user-pass-verify" directive. This allows servers to make calls back to the UH VPN API to check whether a user is indeed authorised to join a network as opposed to just relying on the cryptographic validity of the connection request.
One final and often overlooked note is that when we started development of UH VPN (the website, server software and client apps) wireguard was still very much in its infancy and as such was not recommended for production use. Therefore, we made a concious decision to use the openvpn3 codebase as our base VPN protocol and build our feature set on top of this library. When testing our applicaitons, the performance difference in most people's use cases is near identical to that of a wireguard deployment. We have a strong development team behind UH VPN and when wireguard offers a clear benefit for our clients in terms of performance whilst maintining flexibility with respect to routing and authentication we will add support for it alongside our openvpn solution.
James.