Envato created this rule -> https://themeforest.net/page/item_support_policy
While some developers do provide support after the 6 month period has expired, they are not obliged to do so. It is somewhat logical that this exists. An awesome product that gets update regularly can mean you can use it for years and years. At the end of the day, you have to think that even if you’re paying $50 for a theme, asking 100 questions over the period of a few years will make those developers have to hire staff or spend day and night answering support questions.
At some point, the developer needs to earn something for this beside the initial purchase price, otherwise, what’s the incentive to release incredibly powerful updates.
Also, if you force authors to provide free, lifetime support regardless of the support question, most likely most authors here would leave.
If you purchase a phone for example, a fridge, a bike, you get a warranty period and a user manual, you can of course extended that for years on end. That principle applies to software as well.
There’s a difference between an OS for example, that provides permanent support for a license, and a software product, which, requires some sort of renewal at one point.