OO is a mean, not a goal in itself. it is a better(?) way to handle the complexity of a program as it resembles the world around us to some extend. More than functional programming does. However as most Arduino applications are not very complex functional programming is adequate to handle it. And writing a good quality (reusable) class is not simple either.
I guess that most people think of a system as just one big object 
[ == end user perspective ]