I had a look at https://source.dot.net/#System.Private.CoreLib/DateTimeOffset.cs,396 and I learned something new.

Equals and operator == (which we use) checks if two DateTimeOffsets points to the same point in time, whereas EqualsExact checks if the DateTime and Offset part of two instances are equal.

var a = new DateTimeOffset(new DateTime(2020, 1, 1, 1, 0, 0), TimeSpan.FromHours(1));
var b = new DateTimeOffset(new DateTime(2020, 1, 1, 2, 0, 0), TimeSpan.FromHours(2));
Console.WriteLine(a == b); // True
Console.WriteLine(a.EqualsExact(b)); // False

So if you look at https://stackoverflow.com/a/14268167/581675
Equals test for the Instantaneous time and EqualsExact tests for the Calendar Time?

Exactly (pun intended). The normal Equals tests is probably the most common scenario to assert, and changing "Be" to use EqualsExact would probably break many tests, although replacing it with "BeSamePointInTimeAs" has some merit.