The scripting needed for them is usually minimal, as such the formal coding methods and sophistication of OOP is not required for such small jobs. Any time spent coding towards OOP is would largely be wasted.

As many Microsites have shown, such projects can still be coded using the procedual method as well, but if you are not careful you will very quickly find that the code becomes messy and that adding features becoming exponentially harder.

This is not to say that OOP is a silver bullet for larger projects. OOP is one of the established tools to help keep complexity under control. but the root of managing complexity still boils down to good judgement and planning.

Regardless of the trends, one should always excercise good judgement and use the correct tool that is best suited for the job.