Why are they falling behind in academics and in college attendance?
They actually aren't academic grades are fairly stable and attendance is rising. School dropouts have been cut in more than half over the last 40 years. On the international level, the US has been slipping mostly due to lack of investment in public schools and a greater than ever disparity between States. The fact that many other countries have been investing more heavily in education and gotten richer over the years makes competition harder on the international level (Europe is no longer a bloodsoaked continent that it was in the 50's, East Asia has developped tremendously in the 70's, the fall of communism made the international community less divided, etc.). The impression of "falling behind" is also caused by the fact that women have increased their participation in the workforce over the decades. While girls and young women always had a better attendance and higher grades on average than boys and young men wasn't such an issue for futur employment since women used to occupy more part time jobs or have shorter carriers than men, but now occupy almost half of the full time workforce and similarly long carriers.
Loss of manufacturing, the demise of the infrastructure and the reduction of traditional male trades (carpenter, construction heavy equipment operator, woodworker, machinist) doesn't help.
This is the reason why, despite the fact boys and young men attend more school than ever before and maintain an acceptable average, we talk more and more about this issue and invest a lot of time, financial and intellectal resources in solving this issue. Back in the 60's and 70's about nearly half of all boys and young men didn't finish high school, but nobody really cared. There were plenty of low qualification, well payed manufacturing jobs to employ them as well as a good network of professionnal school to train construction workers, farmers and the like. Today, outsourcing and especially automation has cut back the number of good pay low qualification jobs. The still operating and manufacturing jobs are most often in high tech domain which require, even for assembly jobs, more qualification and thus higher diploma.
In resumé, there is nothing specifically wrong with boys and young men. In fact they are more competitive than ever, but the competition has gotten a lot harder both on the international and national level which gives the illusion that they are doing bad.