So that singing the alphabet song we learned as a child is more melodic.
As a very young child, I remember thinking that "LMNO" was one letter, until I watched a Sesame Street segment which explicitly addressed this misconception. Since this segment exists, I clearly wasn't the only child who got confused.
my know I now z y x
me with sing you won't time next
z y x, w
v u t
s r q
p o n m
l k j
i h g f
e d c b a