Regardless of what past generations have had to say, I'm with hereyago. There are a number of reasons for this trend, though, and having seen it day in and day out for four years of public high school I had a long, long time to wonder why my classmates were such dingbats.
Reason 1: A lot of people ask themselves, "How is this going to help me in my life?" and when they can't answer that they rebel against the school. That question isn't about the diploma - that has undeniable use - but about the classes themselves. It's hard to focus on the goal when you're in a whole bunch of classes you dislike and can't understand the purpose of.
Reason 2: Kids don't like to be forced to do anything. They're forced to go to school, on average for seven hours a day (that's what it was in my high school anyway). Seven hours is a long, long time and it feels a lot longer when you're being forced to do something.
Reason 3: Some kids just don't get it. I mean that literally, they just don't understand the subject matter and for one reason or another aren't receiving the care they require. In that situation school becomes torturous; every day going to to the same place and failing in the same way in front of the same people. Sound like your idea of a good time? How about useful?
Reason 4: And there's the stratification. Cliques, clubs, and gangs rule our high schools, even in places where there is no violence. There's a very set and ordered social hierarchy at most public high schools and it is stifling to put up with. It was one of the chief reasons my own high school experience was poor. At some point, if you're halfway intelligent, the idea of spending another minute around a group of people who idolize the girl amongst them who looks the most like Britney Spears is rather akin to rolling in a pit sprinkled with broken glass and salt.
So there you have it. That's what's going on in high schools today and those are the primary reasons kids don't want to go. As for assuaging these situations, well, there are a number of alternatives - none of which has ever worked very well.