I suspect it has to do with supporting boys already in the program, who are pursuing Eagle rank. With a waiting period of 6 months Life-Eagle, 6 months Star-Life, and 4 months First Class-Star, the worst-case drop-dead date to achieve First Class in an LDS unit would be the start of September of this year, so boys entering the program at the start of this summer could realistically get Scout, Tenderfoot, Second Class and First Class over the summer, and achieve Eagle by the end of the unit charters in a year and a half...
Thanks for the explanation.