Outstanding track runners can become high level NFL performers (Bob Hayes, Reynaldo Nehehmiah, Willie Gault, Darrell Green), but you will not see the reverse, football players becoming world class track runners.
The skill, to be among the fastest in the world, is just too rare. The ten fastest guys in the NFL, after a full year away from football, working with Olympic coaches, would make two slow relay teams, each with one alternate.
There's a big difference between the fastest ten sprinters in the country and guys in the top 100 below them. NFL "speedsters" are, at best, in that top 100 below them, and would trail the top ten in a race very noticeably. A relay compounds the talent disparity, multiplying it by four. Each guy would fall further and further behind.
It's the same with NFL "strongmen," in comparison to Olympic weightlifters. They are weak by comparison to real weightlifters.