Anybody know why it's impossible to book an exam slot before Jan 1st?

Usually, slots can be booked a few hours in advance and the schedule let's you select the preferred slot based on the proctor's language. No language has availability in the next few days. Then starting from January 1st, every language has an abundance of available slots.

Is there a glitch in the system or is there another reason that no exams can be taken in the next few days?