I've been testing VPN services and somehow every one with a client has written their own. Proton, Windscribe, IVPN, Mullvad, AirVPN, NordVPN, and the list goes on.

Don't these services all do the same thing? Connect to a server to get a list of servers, then use WireGuard or OpenVPN to make a connection, and have some fancy stuff like split tunneling or a killswitch. It should just take configuration by adding profiles per service and it should be possible to use the same client.

What am I missing?