Besides corporate VPNs, typical consumer VPNs are also set up to allow LAN access. Your average joe-smoe would be annoyed if their network printer stopped working every time they turned on their VPN to watch netflix movies or whatever.
Saying "all RFC1918 addresses are available over here" is quite a cocky and obviously broken thing to do, unless you're dealing with a corporate device which is paranoid about leaking traffic to other networks.