To be clear, if you purchase an item and there is a demonstratable issue e.g. it’s broken, bugged, etc. then you absolutely have ways of getting a refund.
I don’t think anyone pretends it’s a flawless model, but it’s a balance of Envato’s profits as much as buyers’ choice, and authors’ earnings.
Certainly part of Envato’s success has come from the balance they achieve between quality and quantity, which no one else has come close to. If they were to say ‘all items must remain at the latest version of …’ then responsible authors may well shut up shop because they are not able to guarantee this, which would be bad for everyone (buyers and authors and Envato), and less responsible authors who would just carry on regardless.
But the main question remains - How would Envato police and enforce this? If you have a feasible solution to this then I am certain that Envato would want to hear it.