While the rules help, an offensive revolution has been coming to this point for the past 40 years. Go look at the all-time Yard/TD passing leaders in CFB. Most are after the year 2000. What happened before that time? Most teams leading up to the early 80s lined up in some bunched run formation like the T, I or Wishbone and just ran down your throats. Coaches up to that point thought of passing as feminine and quoted the ol "3 things happen when you throw the ball and only 1 is good" Passing was something they did out of necessity in long yardage situations or as a play action/trick play and since they didn't rep it as much as their running game they weren't very good at it. Pass percentages back then were horrible, if you got over 50% you were considered "elite". Hell, the great Joe Namath hovered around 50% for his career, Terry Bradshaw 52%.
Guys like Bill Walsh, Don "Air" Coryell, Mouse Davis, Lavell Edwards and Hal Mumme came along and made more of an emphasis on the passing game with their passing systems and percentages started to rise. Needless to say, even with their success in the beginning other coaches were hesitant to do what they were doing. You hear stories of these guys giving clinics early in their careers and coaches getting up and walking out en masse as they were talking. They wanted no part of what they were teaching. Coaching isn't a stable occupation and they saw too much risk in throwing the ball to win.
Walsh would go on to build a dynasty with a weak armed QB named Montana at SF, and once he did his coaching tree would spread through the NFL. Look at CFB, the Big 12 was a LOS slugfest before Leach went to OU with a transfer QB and they went on to win the NC running his offense after he left for Tech. The numbers speak for themselves, 5 of the top 11 all time passers in CFB are Air Raid QBs, 2 of them are Run and Shoot QBs and 1 a BYU QB.
Coaches like Urban Meyer and Sean Peyton have been to Mumme clinics. Mullen is rumored to have gotten with Leach to discuss his concepts. You keep it simple for the offense while making it complicated for the defense and see who plays faster late in the game.
Coach Darrell Royal once said "A thinking player is a slow player, and you can take that to the bank"

Defenses are still fast/talented, they're just being overloaded with information and out repped by today's offenses. Paralysis by analysis as they say.
"I don't fear the man who practices 1,000 kicks 1 time, I fear the man who practices 1 kick a thousand times." -Bruce Lee
Troy Aikman once boasted that he and Michael Irvin could go outside right now and he could hit Michael with the ball with both of them being blindfolded.

Patterson, Muschamp, Mason, Odom, Pruit, Strong, Pelini. All top DC names recently. All of their defenses being taken to school. Better get on the bus and get a good Offensive guy as your HC, because with scoring and QB efficiency at an all time high, it may be a while before defenses catch up.