In fact, it would be worse for them, because if everyone is paying as much as they can bear for internet, and they have given some the option to opt out of an unneeded service, then they will lose money.
Assuming they have total monopoly power.
Only a small fraction of people use VPN, so the monopoly price in a world with net neutrality basically ignores those people and charges the optimal price for everyone who does not use VPN.
However, in a world without net neutrality, the company is able to charge a different price to those who want VPNs and those who don't (this is price discrimination). So it keeps charging the old price to everyone else, but adds on a surcharge only to those users who want a VPN. In this simple example, it makes an extra dollar per month per VPN-user.