From the customer's perspective, it would kind of suck to buy an app because of a certain feature that, from your point of view, gets broken by an upgrade, and be forced to do that upgrade, because the developer fixed a bug or feature that is of no concern to you. Remember, the user is buying a license for the current version of a piece of software, not a SaaS subscription.

Example: I was searching for a tool for file deduplication. Looking at some older screenshots and the current trial of a certain tool, I realized that this was now less geared towards power users, with UI changes that made the tool look better for inspecting a few duplicated pictures but unsuitable for using lots (thousands) of files. Imagine being the user who bought the tool for more serious use, and is forced to "upgrade".