What? The whole idea of the prefix system is that it’s granular enough that you can describe any size as up to 100s (or 10s of common sizes) of any prefix.

Think of it as scales: Metres is the unit for things people sized (including kids), decimeters for things hand sized, centimeters for grit sized, etc.

Other scales are mostly an extension of the system: Kilometers is “away” sized, millimeters are tiny sized, and following the convention of 10s makes for easy to remember and translate conversions, although I’ll admit that they aren’t inherently more convenient than other measures.

Similarily: foot is stick sized, an inch is pebble sized, but the imperial system then doesn’t easily convert between other common human experiences. Talking of things seed sized becomes weird fractional math, figuring out how many steps it is to the next town (miles I’d argue is “trip” sized) gets weird. And when you need higher precision you end up in fractions of a larger unit rather than convenient ones.

The size of an atom is about 100 pikometers (10e-12 metres) and a molecule about a nanometer (10x the size). In US customary an atom is about 1/262144 (2^18) thou of an inch, and molecules about 1/2048 (2^11) thou of an inch. And if we want it compared to miles or feet, we’ll have to redo the calculations from scratch with loads of danger of messing up conversion numbers.

Besides, most of the benefit of the metric system is that the standardised scale prefixes makes it very easy to correlate all other physical constants. Speed of light is just under 300 km/s, which is about 300 m/ms or 300 mm/ns, or 200 miles/second which is about 1000 ft/ms or 10 in/ns (not to mention that rounding errors are larger in customary)

EtA: I do wish we had a base 12 math system though