This is, again, not necessarily the department. It could be that the government has decided, as opposed to making a decision to cancel the program or to extend the program on an ongoing basis, to extend it for one year. The decision has been made in that case to extend it by one year, and for that reason it could come before supplementary estimates for a couple of years in a row.
It's not necessarily how departments are deciding whether they should or not; that could be an overall government cabinet decision.