Imagine someone selling you a Mercedes worth 60,000 euros for 30,000 euros. While this can happen with used vehicles, this particular car is as good as brand new. No dent, not a single scratch, no wearing parts.
Such a deal would be an economic miracle.
Yet this is exactly how used software works. You get the same product as customers who pay the full price, with all functions and features and every line of code working exactly the way it did on the first day of use.
Surely there must be a catch? No, there is not. This is because hardware wears out, but software does not.