CTE cases will go down now that the NFL has developed a concussion protocol requiring players to sit out until they are fully healed. You can have 25-50 concussions over the course of your career, but as long as you take down time and fully heal after each one, your brain will be none the worse for wear. It's coming back from them too early and sustaining another one that causes CTE and other forms of brain damage.
And you know this information how exactly? I was under the impression that they still weren't sure how and what caused CTE exactly or how to prevent it. Sure there's a link between head injuries and CTE, but to say that only getting another injury before the last injury is healed is what causes CTE, I find that hard to believe they know this to be a fact.
According to the below site, it's thought that even hits that don't cause any symptoms of a concussion could still lead to CTE. If that's the case, then no the concussion protocols the NFL has in place won't prevent CTE even if they are followed appropriately.
http://stopcte.org/whats-cte/what-causes-cte/