Some of the documents are here. As document 61 of the trial, the government motion for bench trial, argues,
There is no constitutional right to a jury trial for criminal contempt
charges resulting in a sentence of imprisonment of six months or less.
Arpaio responds in document 62 that
Defendant Arpaio acknowledges that there is no constitutional right to
a jury trial for defendants charged with “petty” offenses where the
maximum sentence does not exceed six months imprisonment,
but continues the argument (the point being that there is no question that there is no absolute right to a jury trial, esp. in the instant case). He argues
Many of the actions of the referring judge will become an issue in the
case, calling into question the objectives and motives of Judge Snow.
A public official’s actions and motives should and must be decided by
an impartial jury of the elected official’s peers.
The court order is document 83. There,
The Court finds that this case is appropriate for a bench trial. This
case focuses on the application of facts to the law to determine if
Defendant intentionally violated a court order.
Essentially, since there is no right to a jury trial and no compelling reason to grant a jury trial (e.g. the court found no merit to his argument that there would be the appearance of impropriety), the motion for a bench trial was granted.
The order cites case law regarding the "not longer that 6 months" rule from Muniz v. Hoffman, 422 U.S. 454; United States v. Rylander, 714 F.2d 996; Taylor v. Hayes, 418 U.S. 488; United States v. Aldridge, 995 F.2d 233; United States v. Berry, 232 F.3d 897.