There are many free VPN services, but they mainly stay in business by selling user data. Running a VPN business comes with costs for hosting servers, developing software, and other operations-related expenses. When providers don't charge to use their services, chances are they're collecting and selling user data. Not only that, most free VPN providers limit data and traffic speeds, meaning your internet connection will be slow and unstable.
It's always better to go with a low-cost, premium VPN like Private Internet Access than it is to deal with the risks and limitations of a free VPN.