If a players hair is long enough that it reaches the jersey, it's part of the uniform and can be used to pull the player down, therefore it's up to the player to keep their hair short.
When you're chasing a ballcarrier with other 200-300lb athletes pushing and shoving you around it is very possible to inadvertently grab someone's hoodie and yank them to the ground. It's not that hard to understand the concept at all and it's obviously a very valid rule to help with player safety.
We need to understand that these are human beings, not machines and just because there is a rule preventing horse collar tackling doesn't mean it will never happen unintentionally.