I'm not American so I would never watch football but didn't Bork join some team and smash all their athletic scores?
It's not a popular truth to mention around here, but quite simply, the level of athleticism in the NFL grossly exceeds the UFC, and the same is true for American Football versus combat sports (like folkstyle, freestyle, or Greco Roman wrestling) at the college level and lower.
Brendan Schaub, Matt Mitrione, Greg Hardy, and Marcus Jones are all former NFL players who at least played snaps before transitioning to the UFC. This is MMA's greatest organization. Bob Sapp fought in PRIDE. Herschel Walker, Wes Shivers, Austen Lane, Michael Westbrook, and Rex Richards are other former NFL players who have had success at the "minor league" level of MMA in organizations like Strikeforce.
That's just the NFL. Then there are dozens of former football players such as Shawn Jordan or Eryk Anders who played at Division I football powerhouses like LSU & Alabama (the latter won a national championship, and signed--but did not play-- with the Minnesota Vikings). If you rummage further, you have examples like former UFC Heavyweight champion Shane Carwin who was a multi-sport college athlete playing at a lower level, but who still impressively earned multiple All-American honors as a Division II football player.
Nobody retires from a UFC career and is suddenly taking snaps in the NFL. Nobody. The crossovers are one-way for a reason. "A-level athleticism" might be tongue-in-cheek, but the reality of the concept is real. There's just flat-out superior athletes in that sport, and in that league.