Well, VPN service providers do have to make money after all. It wouldn’t make sense for them to let users keep using their free trial over and over again. So, they will only allow you to use a free trial once.
Of course, if you are crafty enough, you could, in theory, use different emails to sign up for multiple free trials. That is if you are not required to input your bank detail.
But VPN providers are aware of this trick too, and if you are caught, you could get banned from using the service.
But then, you can just pay for the service. Many providers we presented are quite affordable.