What's important here is that the standard measurements evolved naturally from people doing and making things. The common lengths were so chosen because they were easy to "eyeball" for craftspeople, and they were lengths that were useful to make things in - not some arbitrary designation based on phenomenon far outside the human experience.

For a person's foot to measure exactly 12 inches long, they would wear a US size 14 men's shoe. Size 47 for the Europeans. So "spproximately the size of a foot" is pretty far off anyway. Most people don't wear size 14 shoes. In fact, people who wear size 14 shoes often have a lot of trouble buying shoes.