Because in the US at least, part of ISPs business model comes from deep packet inspection of customers websites, dns queries, habits and subsequent selling (or

Because in the US at least, part of ISPs business model comes from deep packet inspection of customers websites, dns queries, habits and subsequent selling (or using) that data. If you have a trusted VPN you can prevent that data and privacy siphoning. "trusted" VPN company is a discussion for another time...