What you are paying for with these services isn't exactly "a VPN"; rather, it's some combination of the following:
- Use of somebody else's computer (where the VPN software is running).
- Use of somebody else's bandwidth.
- Additional anonymity from your traffic being mixed in with other people's traffic which is being routed through the same VPN.
It's somewhat foolish to pay for a VPN service if you only care about (1) and (2) because it's much cheaper if you just pay for those services directly. However, (3) is the real value add.
Routing all your traffic through a VPN that you control and which is for your exclusive use offers no anonymity whatsoever. But if many different people route their traffic through the same VPN, then it becomes harder for the adversary to determine which traffic from that IP can actually be associated with you.
If you don't need (3) or the service doesn't provide (3), then there is no reason to pay for a VPN service. Even if you do need (3), it would be a mistake to
rely on a paid VPN for that purpose (because, among many reasons, you can't actually prove that it is doing that).