What reasons are there that you know of? I imagine very accurately perforating 135 and spooling it into cassettes would require greater technical skill and effort than would cutting 120 size film and spooling it onto rolls with backing paper.

As a student, using E6 film is already a luxury and purchasing such a quantity of film is simply out of the question. Given the price at which wittner is selling the bulk rolls of 135 aviphot chrome film I could well imagine the possibility of a cheaper sheet film alternative compared to Fuji's current offerings of E6 film at around 50 euro's for 20 sheets.