The Hand_off. Finally, state your willingness to help out with the transition. You don't need to go into great detail (and definitely don't promise anything you can't deliver), but a couple of lines stating that you'll ensure a smooth wrap_up of your duties will show that you're in the game until the very end. Obviously, feel free to adjust this a bit based on your experience and your company culture, then submit it via the typical procedures at your company.
However, it could also be the reaction if your company is approaching or is currently in a busy season and needs the additional staff, or it's experiencing unusual circumstances, like a hiring freeze, which would prevent it from replacing you entirely.