This regulation ensures that whoever sells the software to the consumer is responsible, and that's the way it should be. The creator of a library doesn't know how his library will be used in the wild, he can't anticipate all possible problems, the product maker can. It is the product maker's responsibility to integrate external components properly, having validated that they are up to standard.
If you're a manufacturer, you can't just pick components at random and then say it's not your fault if your product doesn't work. That's why manufacturers have whole teams of people working to ensure that what they receive from a supplier is up to spec.