Despite their natural fear of critiquing a monarch, Achashverosh’s advisers had the added restraint of having seen the paranoid king dispose of Vashti. The Talmud (Megillah 16a) clarifies that Achashverosh’s officers did not respond out of a great love for Mordechai, but a great hate for Haman.
The Ben Ish Chai traces their motivation to the suspicion that Haman fathered the advisers’ illegitimate children.
According to R’ Dovid Feinstein, this hate was motivated by the very jealousy Esther had hoped to inculcate among Achashverosh’s advisers by inviting Haman to the party.
The Maharsha proves that the advisers did not act out of good feelings toward Mordecahi by pointing out that the advisers used the general, diminutive word davar (“thing”) instead of the honor and glory Mordechai deserves.