If the local ISP has a 100% chance of monetizing my data and the VPN provider has anything less than that, then it's still a win.

(Longer answer: This boils down to the weighted probabilities; if the ISP was meaningfully regulated such that it was legally restricted from doing certain things with my data, that might matter, and one should also play in the exact likelihood that either party is selling my data. In my case the weighted probability is wildly in favor of a VPN, but I suppose I can imagine situations where that wouldn't hold.)

It’s their business (value proposition) to not do the same and most explicitly commit to that. They also get third party aidiots and publish results. This isn’t fool proof but it’s better than trusting Comcast or ATT or whoever.

I VPN to a $5 vps in a distant country. I kill and move/re-up it once or twice a year.

They probably could sell my traffic, but I estimate it (based on vibes) as being less likely than for most other intermediaries