Concussions are not your typical sports injury
If a football player broke their arm or if a volleyball player sprained their ankle one part of the treatment is inevitably to rest. Really any injury should be followed by a resting period of that body part. If an athlete was to get a concussion treatment would, once again, call for rest. However, a concussion would call for the resting of the brain. If an athlete is on crutches or has an arm in a cast they still can talk to people, watch TV, get emotionally upset, read books, go to class and a number of other activities that will not lengthen their recovery time or hinder their ability to rest their injured body part. Concussions are a different story.
There is no cast for a “broken” brain
According to the Mayo Clinic, currently the best treatment of concussion is both physical and mental rest. They suggest to not do any type of physical activity or mental activity that requires concentration such as: playing video games, watching tv, schoolwork, texting and reading. The only treatment options in the form of drugs that the Mayo Clinic suggests is over the counter Acetaminophen (Tylenol) or Ibuprofen (Advil) for headaches following a concussion.
What it boils down to
Even though doing what the Mayo Clinic suggests has been shown to speed up recovery (compared to not doing what they suggest) actually resting the brain is much easier said than done. If a student athlete was to get a concussion how can you expect them to not text their friends, to not read a book, to not laugh at something funny or to not go to class. These are such regular occurrences throughout our daily lives and to completely stop can be very difficult for some people. What is takes is a dedication to the recovery and focused mind to simply rest. But don’t focus too hard!
Why are concussion so difficult to treat?

Because it is brain damage, duh. People who chose to do risky sports, etc. that are known to cause brain damage, must accept brain damage as a part of the sport and stop whining to the rest of the world.