They’re at those levels of reputation for a reason. The Mandates are transferable between characters so then once you grind out Revered on one character, you can give them to other characters to speed up the process. It’s a special reward for working really hard to get to that level.
Also, Writs and Mandates won’t stack, so getting a writ earlier would only help a little to get to honored, and then you wouldn’t be able to use the Mandate to get the 100% boost anyways.