For shoes, I would think there’s just too much variation in foot sizes, foot shapes, and runner’s weights to even consider that.
Cycling similarly allows picking the bicycle frame to match the rider’s body. It does have a minimum weight for bicycles, though (6.8kg, which is high for current tech. Given deep enough pockets, 2.7kg was possible in 2010. See https://www.tririg.com/articles.php?id=1035_Worlds_Lightest_...), and regulations that effectively forbid recumbent bikes.
In some cases, flexibility also is there for historical reasons. In soccer, not even field size is fixed (with exceptions for top levels) for that reason (fields inside athletics tracks tend to be longer and less wide than fields inside stadiums specifically built for soccer)
A soccer field must be rectangular, but can be anywhere from 45 to 90 meters wide and anywhere from 90 to 120 meters long (https://resources.fifa.com/image/upload/spielregeln-2019-20....)
So, minimum size is 90m × 45m, maximum size is 120m × 90m. Area-wise, that’s a factor of 2⅔.