Sports is a domain for the young. This makes the most sense from a time-commitment perspective. To truly follow team sports in the 21st century, a lot of work is required. The young have relatively more time because, quite frankly, the young don't have many important things to work on yet.
I think working on something important (in the broadest sense of the term) is vital for establishing a sense of purpose in life. Since being devoid of anything actually important to work on is a defining condition for many students, it's not a surprise to see so much time during the school years spent on things creating busyness such as obsessively following sports.
Of course, anything a person spends a lot of time on becomes important. It is a semi-application of Annie Dillard's well-known quote from The Writing Life- 'How we spend our days is of course how we spend our lives.' Days spent following sports become a life spent following sports and, well, all life is sacred, even if a life is spent supporting Manchester United!
