People not fully invested in the win at all costs mentality which became uniformly pervasive were nauseated by the NFL fan base when Oakland and Pittsburgh both fielded teams designed to win by intentionally injuring players on opposing teams. Not only did the NFL drag its feet on addressing the issue...the revolting fans they retained didn't even demand it.
The fan base at that time had become so inured to unsportsmanlike behavior that they didn't even realize that what they were allowing to go on in their sport caused people who didn't watch or who were casual watchers to view them with disdain.
The NFL didn't just gradually fall into a league of felons. It had a sudden jumping of point, and that was it.
Where they are now was both predictable and inevitable.
It got worse in the late ‘80’s, as the mentality of the University of Miami attitude gained a foothold in NFL.
The ‘70’s Raiders and Steelers may have been brutal, but they would not have put up with the sideline antics of their teammates like teams do now.