There was a couple I had heard about who bought an electric car. They took their electric car to a shop that promised more millage (or faster charging, I can't remember which). As it turns out this custom modification killed the battery in a few short years, when it was supposed to last much longer. The couple was not happy with their purchase, and they never connected that the work they had done was related to their vehicles shortcomings.

If we are charitable in our interpretation of manufacturers positions, keeping customers from "tinkering" with devices maintains the brand's image and prevents unexpected product failure or safety misshaps.