Right, but other services like gmail, who run in the background at the same time, are simultaneiously seeing the same endpoint of the VPN. Whats stopping them from comparing logs for profit? Google knows its me, I'm signed in. Same thing with any other app I have that uses a paid subscription. If someone that sees my credentials also sees my VPN endpoint, they can then share the knowledge of "who is using that endpoint" with those who want to know elsewhere on the web (those sites who I have not shared credentials wit).Over a VPN, the sites you visit see the IP address of the endpoint of the VPN, not your IP address, and it's not coming from your ISP.
Look at it like this. You mail a package using the U.S. Postal Service (which is like your ISP connecting to the VPN) to a courier (who is like the VPN) who then flies to Paris and mails your package for you to the destination address using La Posta in France. La Posta just sees what mailbox the courier mailed the package from, they don't know how he got it.