Yes, the customer doesn't get to keep the latest version if they stop their subscription, but JetBrains needs some reasonable hook to cover support costs, and quite frankly, their software is relatively cheap in the commercial market and generally works as expected.
It also addresses the concerns of those who claim "they'd be willing to pay more". If you decide to stop your update subscription, you have the option of getting a perpetual license for the latest version at that point by simply buying a year's worth of updates.
If there's a better option that keeps JetBrains in business and customers happy, I'm sure many would like to hear it.