411A:
Because, that is the way it is done in the USA. However, as I fly outside the USA most of the time, I prefer meters (metres
)
Outside the U.S. I find 5+ n.m. for circling protection to be far preferable to the FAA's 2.3 n.m. Since your Part 121 operations are outside the U.S. most of the time, do your agust FAA inspectors and handlers test you on knowing when an airport is 2.3 for cicling and when it's 5+ ("+" is because PANS-OPS, unlike TERPs, wisely increase the limit with airport elevation).
If the feds (and the airline trainers) don't train and check to those significant international differences, then they are not doing their job.
And, what if the Jepp chart for ABC Airport in Country Z doesn't proclaim either TERPS or PANS-OPS on the lower left margin of the chart?