>Because a VPN in this sense is just a glorified proxy. The VPN provider can see all your traffic, and do with it what they want - including logging.
This is a tautology. If you use it as a proxy, then its a proxy. VPNs arent for this, and so are bad at it.
VPN use case is either to securely leave a network (hotel Wi-Fi, airport wifi) or to securely get to a network (home resources, corporate resources). If you want a proxy, find a proxy.