The real ME writes:

The question I have is, why does NOAA use knots on their weather
charts instead using mph? Is there a historical reason for this (i.e.
that is the way it has always been done) or a scientific reason for
using knots?

1 knot is one minute of latitude per hour, which simplifies navigational
estimates. Under sail, one estimates potential speeds from wind speed, and
thus the knots of wind translate with simple calculation to chart divisions
you can potentially cross with your boat.