Earlier quoted context omitted.
Many of those unelected bureaucrats are experts in their fields due to their ability to focus for entire careers.
Is Congress not capable of listening to those experts and then publicly debating which of their suggestions to implement?
2. Politicians, per definition, are elected to represent the interests of their constituents. Many constituents disagree with experts (climate change, for example). QED, there is little motivation for politicians to listen or follow the advice of experts, especially if an expert's conclusion is not popular.