Because dragon ball servers were born from game called Dragon Ball Z: Buu's Fury and in this game outfit sprites were made 32x32 and since every dragon ball servers are based of 70-100% stolen sprites so year after year everyone used same character design sprite which is (EXAMPLE)
View attachment 39387
Everyone got used to this style and size so thats why there is no 64X64 48x48 sprites usually its 32-4/32 not including characters like (buu,cell and etc)