It could be a couple of issues:
1) Depending on the site and type of work, the fall could be a slow time for them.
2) Not knowing your background, training expectations for DOE (10CFR835) is a lot more intensive than commercial. If someone has never been in that program, they are more likely to take someone who has (returnee).
3) The budgets for DOE are usually approved and released in October, so this could be a lag time between approval and funds reaching the different projects.
I hope this helps your understanding.