Why do so many language schools offer courses of weird fixed lengths? For example 1 year 3 months starting in October. What if I just wanna do one year?

I find myself in this pickle. I just wanna do one year but I keep finding schools that offer 1 year 3 months or 1 year 6 months starting in October ( when I wanna start) and instead the only 1 year course starts in April.