Yeah, this just follows the rule of if its free, you are the product, not the customer. You're going to get ads and relinquish your data in exchange for the service.

For proton, I assume they have a free tier (I don't know I pay for it). So I guess they let people know to push adoption or get people to make the jump, but the assumption is they have some conversion rate to paying customers. For those that never want to pay for email as their usage scales, they're better off staying.