You just middleman the vpn authentication via wifi - by spoofing the wifi router you THINK you are connecting to, but it's not really because its just emulated with a stronger signal so your device thinks everything is fine.
If you try to do that, the VPN client will notice that the spoofed server isn't presenting a valid certificate or doesn't use a valid key, and refuse to connect. Same reason you can't "just" middleman an HTTPS connection.
Besides, there's no need to spoof. The point of the VPN connection is to protect against the wifi router (even the legitimate one!) reading the traffic. By spoofing, you're just replacing a dodgy wifi router with another dodgy router.
Many PC antivirus/firewall programs do it right now.
Entities not in control of your PC can't MITM an HTTPS connection, barring a catastrophic bug. And it is catastrophic. If you have a way to do this, please tell everybody because it's going to be the next Heartbleed.
The entire point of HTTPS is to prevent stuff like you're describing. And it does work, for the most part. Bugs happen, but they get fixed as they're discovered. It's definitely not "extremely easy."
Please go read up on this stuff before speaking authoritatively:
More succinctly, the phrase "man in the middle" kinda loses meaning when the man in question is your own computer.