The JavaRanch had a very interesting discussion on just this topic:
http://saloon.javaranch.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic&f=78&t=003738
I agree that we don't always need a framework like Hibernate. And that logic applies to all things. Like, why do you need farmers when you can grow your own food? Why do you need to buy a car from a dealer when you could build one yourself?
Some people think it would be silly to not build a car from scratch, or to buy milk when they could just milk a cow on their own. Those people tend to prefer to just use JDBC and avoid frameworks.