That and college football was easier to dominate without any black players on the field. Still love Atkins, but I doubt he’d be as dominant in an integrated sport. Not to say that he wouldn’t still be great, but some say he’s the best DL of all time and I don’t know how you can come to that conclusion when the competition was watered down.
A part of me agrees, but you're overlooking a significant reality. Ethnics aside, players today have their nutrition carefully monitored and planned. Training is far better at maximizing strength, agility, speed, and relevant technique - such as reaction to ball hikes, and play recognition. Back in Doug's day, natural talent reigned supreme. IIRC, Doug was a drinker. So was (forgot name) Super Bowl Packers receiver, who got drunk the night before. Not anticipating playing. But the Receiver one got hurt. Back scores 1-2 TDs IIRC. Today, players are practically tailor-coached on a level the likes of Atkins never even dreamed about.
Now, as for the Black players, they did have some natural advantages, that still exist today. Which is why many pro sports rosters in general exhibit this by the sheer number of Blacks on teams. As a matter of fact, back in the mid-late 1960s, again, IIRC, that's when you saw mainly White players using steroids to sort of even the odds of competing with Black players. Just the same, some folks, ethnics notwithstanding, you will always have players that are simply extraordinary. Jim Thorpe (Native American), Wataru Misaka (Japanese-American NBA player), and the rise of athletes of color in swimming, gymnastics, and other traditional White only bastion sports. You also have Extraordinary players like Rob Gronkowski, Raymond Berry, John Havlik, Jerry West, and so on, and on, including Doug Atkins. Again, ethnics not withstanding, you will always have those very special individuals, perhaps mutants, that stand out. In the case of the USA, the country didn't appreciate or utilize her full potential until she got out of her own way and let everyone compete. To a large extent, she still needs to get out of her own way.