A few points
- If you don’t have control of the network, there are all kinds of nasty ways to proxy your traffic and create man in the middle attacks. https can be broken and inspected.
- The encryption strength of ssl is partially controlled by the site you are visiting
- Not all your traffic goes over https
- Even with https an attacker(or an ISP) can track what sites you are visiting
Strong VPN encryption is much harder to break or inspect. It also gives you more control.
Just like everything else, it depends on how privacy-centric/security-centric you are and which risks you care about.