This is because people don't realise that there are two axes on the simplicity/complexity graph, not one. So they're operating on different definitions of 'simple'.
You can make the development experience simpler, and/or you can make the software simpler.
Usually a change to one will have an inverse affect on the other. Bringing in a library will almost always make dev simpler (unless the API is more complex than whatever it's abstracting, which only seems to happen in JS land), but it's also guaranteed to make your software more complex (unless it does exactly what you need with no config, and nothing more).
