It's not about inheritance, it's about specificity. If you have a generic module that specifies

  padding: 5px;

And you actually the bottom of your element to have more padding, you need to be able to do adjust the bottom padding independently

  padding-bottom: 10px;

Otherwise, you'd be required to tightly couple your our padding requirements with the defaults of the original module

  padding: 5px 5px 10px 5px;