Is there a strong reason to close applications in January?
I’m only familiar with the deadlines for economics graduate school, but for that you get decisions back from graduate school in February-March along with the funding package. Therefore, it would be useful to be able to apply for this depending on the funding package you receive (e.g. if you are fully funded you don’t need to apply, but if you are given little or no funding, it would be important to apply) .
The main reason has to do with capacity/turnaround times. Our experience is that a lot of candidates apply very close to the deadline, and prospective grad students typically have to accept their offers in mid-April, so if we had set our deadline in, say, mid-March instead, this would have given us only c.4 weeks to process these applications (which as it happens is already going to be a busy period for the relevant team members for other reasons). The earlier deadline gives us more wiggle room, although it does come at the cost you highlight. Candidates who don’t apply in time for our deadline and find out in February/March that they’ll require funding may want to consider applying to the Long-Term Future Fund.