it's simpler and a lot easier for another engineer to look at and understand later, so they can verify that it's right or change it if it's wrong or we decide to do something a little bit different. it's also been reviewed and tested by a lot of people working in a lot of cases that are all a little bit different from one another, so the odds that their code is correct are better than the odds that my code is correct, all other things being equal

It's easier to understand, easier to review for correctness, and less likely to cause problems with additional changes in the future. Even though it sounds counterintuitive, software developers generally try to write as little code as possible. Any code you write is a potential liability that has to be maintained, so if you can instead just call code that others have already written and that has been tested, you'll want to do that. (Note that "less code" doesn't mean fewer lines of code, it means less logical complexity, which is often, but not always, also less in terms of characters/lines)