There are reasons boxing is not as popular and head injuries is not necessarily at the top of the list. At every level other than professional (where knockouts are encouraged, because that is what the American public wants), Boxers wear headgear, they are not allowed to fight until they pass concussion tests, and it is generally very safe (a lot safer than slinging rock on an urban street corner. Yes, a dispproportionate number of true boxing gyms are in urban environments). Boxing is down for four reasons...
1) The most historically prestigious division sucks. There is very little action in the heavyweights except for a few flurries here and there. Much of what they do is circle around the ring, throwing a few jabs per round. The two best Boxers happen to be brothers and refuse to fight each other. It's just not that entertaining to the general public.
2) Lack of Characters/Personality - Fans cannot get behind or relate to today's boxers like they did Ali, Foreman, Liston, Homles, or Tyson.
3) International Growth and Talent outpaces American - See Olympics, Summer, 2012.
4) Perceived wide-spread corruption.
Likewise, football is much safer at the youth level. The players are virtually equal in size and do not approach 150 lbs. (by rule), let alone averaging 280lbs of solid granite muscle. There are certainly some freak injuries, but concussions are typically monitored to the nth degree at the lower levels and they are not allowed back on the field until they are cleared. You are certainly correct that a concerted effort needs to be curtailed at higher levels regarding head trauma, but an argument can be made that awareness of these injuries is as high as it is because the sport enjoys such a degree of popularity. As I said rule changes will certainly go into effect before the golden goose is cooked.