Because all of the students are applying for student visas at the minute. They're always busy this time of year.
Yeah, this is the same for US student visas too - June, July and August are the busiest times of the year. The US embassy in London makes everyone go for an interview now (since 9/11) and when I applied for my first US visa in 2003, there was a 2-month waiting time for an appointment, compared to the usual few days (I booked the appointment in May and didn't have the interview until July - I eventually got my visa and booked my flight about 3 weeks before I was due to leave)!
Then, when I entered the US for the first time on the visa (the week before classes started in August), there were so many students going through immigration that they had a whole separate line for them... the normal immigration line took about 5 minutes to go through, but the student line took almost 3 hours (I even missed my connection and had to wait for a later flight)!
However, when I re-entered on my current student visa 2 weeks ago, I got through the normal immigration line in 2 minutes because there were no other students entering the country yet
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