We do not sell lifetime licenses and do not plan on adding them at the moment.
When you purchase the plugin you get a license that includes 1 year of updates. When that year is over the license is automatically renewed unless you cancel that subscription. If you cancel the subscription you can keep using the Premium version you’re on when the license expires for free but won’t get updates or support anymore.
We have this type of license in place because we continually keep improving the plugin and releasing new features. There’s also ongoing support, of course. We believe that this type of licenses pushes us to keep innovating and will benefit the customer as well.