With a backlog of work to do once you return. Its not like an office or factory suspending operations because there is no work. Many of these people have deadlines that they won't be able to meet without a great deal of effort and likely overtime (if granted). So not only does this shutdown give them a "paid vacation" it's going to pay extra so that the work can still get done close to on time.
… and don't forget the politically charged atmosphere. You're still going to hear about how government agencies don't work but most of the attackers won't mention things like e.g. the way the VA was making progress on their backlog until October 1st:
