A reason for choosing OpenVPN over allowing direct SSH connection is typically that the site has all the computers on an internal network, behind a firewall. These computers are without an externally accessible IP address. Thus, no direct SSH possible. Then you set up a single OpenVPN server behind the firewall, and you set up the firewall to forward the OpenVPN ports to it.

Now you use OpenVPN to get access to the network, and after that you use SSH to access the computers on the network. Thus, you have ssh inside VPN, not so much for added security but because that's the login method of choice for most people anyway - and you also have encryption when moving around on the internal network.