…when Democrats defend their home state industries at the possible expense of the nation as a whole, there’s no sane Republican to counteract them. While the linked article discusses the medical device tax, this applies to many issues: I expect coal-state Democrats to vote for keeping their constituents employed and existing businesses running, but there aren’t any Republicans who are willing to vote on the other side (anti-coal in this case).
As a result, Democrats will often have the overwhelming majority of their caucus on one side of an issue, but even when they were in the majority, they couldn’t get a majority of the House or Senate (or break the filibuster).
This is a problem.