Notes on the Bible, by Albert Barnes, [1834], at sacred-texts.com
It was a settled principle of the Persian government that "Royal Benefactors" were to receive an adequate reward. The names of such persons were placed on a special roll, and care was taken that they should be properly recompensed, though they sometimes waited for months or years before they were rewarded.
The honors here proposed by Haman were such as Persian monarchs rarely allowed to subjects. Each act would have been a capital offence if done without permission. Still, we find Persian monarchs allowing their subjects in these or similar acts under certain circumstances.
It is quite consonant with Oriental notions that Mordecai, after receiving the extraordinary honors assigned him, should return to the palace and resume his former humble employment.