Willard's lewd conduct arrest last week prompted concern that the "unfortunate circumstances" would distract from the show that debuted last week, Kerger said.
PBS has high hopes for the new show, which is intended as a companion to its highest-rated series, "Antiques Roadshow."
Within 24 hours of his arrest, Willard was replaced by Mark Walberg, host of "Antiques Roadshow." Walberg's new voiceover was done in time for the second episode airing Monday, Kerger told a meeting of the Television Critics Association.
Willard's firing took place as PBS once again confronts efforts by Republican lawmakers in Washington to cut funding for the Corporation for Public Broadcasting, which provides 15 percent of public TV's budget.
Best known as the announcer in the film "Best in Show," Willard was arrested Wednesday night for investigation of committing a lewd act. He was taken into custody by police doing a routine check at a Hollywood adult theater.
By midday Thursday, the 72-year-old actor was fired from "Market Warriors," produced by Boston public television station WGBH. He provided narration and was not seen on-camera.
The Los Angeles City Attorney's office determined Friday that Willard's case was eligible for a diversion program that will keep him from being formally charged with lewd conduct if he completes the required courses. Willard will pay $380 for the program.
Willard said in a video posted Thursday by celebrity website TMZ that his arrest was a misunderstanding and denied wrongdoing.
Willard was nominated four times for Emmys for guest roles on TV's "Modern Family" and "Everybody Loves Raymond." In Pixar's 2008 hit "WALL-E," he voiced the character of Shelby Forthright, the CEO of a ubiquitous big-box chain called Buy'n'Large.
In addition to "Best in Show," Willard has also appeared in other Christopher Guest mockumentary films, including "This is Spinal Tap" and "Waiting for Guffman."