I'm not well-versed on the topic, but I'd guess that an abrupt change in protection could lead to more injuries in the short-term.
Ah. That's a good point. I know nothing about football. I just assumed that they could make changes if motivated given the enormous amount of money it generates.
Changes are made regularly, often to encourage player safety. But I think you can only make a game so safe when it's predicated on tackling people.