Well the main reason is, all people would want to go to the direct mirrors. So that means a huge flow of people(prolly like 700 or mor), on one server would be downloading, and the server's bandwidth would extremely low, then die off from the admins for too much bandwidth being taken. Then people couldnt download for another month or never, but, if they did still keep it up theyd still take up more and more bandwidth with more and more people downloading. And with those 700 people on at once, youd get an extremly slow download for a mod like this.
Now, if you have a lineup, your only have like 100 dling off the server at one time, when their done, the next can go and your keeping it down at a steady rate. This gives a faster download.
Keep in mind, esf is a big file for a dl, and so with more people, it would just go slower and slower a dl by the second.