People have all kinds of ways they stack wood and for all types of reason but the principle is the same one. Some people just like their wood pile to look nice and decorative. Others do not care.
Stacked wood is also easier to access, and it fits nicely in a woodshed. When it's stacked, you can have certain types, sizes or ages of wood in different rows. It's also something of a pride thing - sort of like neatly arranged tools in your workbench.