Legacy of the 1970s-1980s attempt to move the US onto the metric standard.
Don't tell people who are annoyed by metric, but all the 'imperial' units we use now are 100% based on metric units. Our metrology has been metric since that time, all the day-to-day usage is derived units.
Which is why an inch is exactly 2.54cm instead of some rounded fraction.
That's actually required by federal law. A lot of commercial regulations in the US require metric measurements in addition to imperial.