Because of Moore's sex scandal, not because of anything Jones can bring to the table.
In 1995 Doug Jones the U.S. Attorney for Alabama won release of FBI files withheld from state and federal prosecutors since the 1963 KKK bombing of the 16th Baptist Church in "Bombingham" which killed four girls aged 11 and 14 and injured 20 others in the church.
Jones learned that in 1965 the 25 FBI investigators had identified as the perps four known KKK members and segregationists -- Thomas Edwin Blanton Jr., Herman Frank Cash, Robert Edward Chambliss, and Bobby Frank Cherry.
"That is a confession out of this man's mouth."
U.S. Attorney for Alabama Doug Jones points toward Bobby Cherry as he delivers his closing argument to the jury. May 21, 2002.
Chief Prosecutor Doug Jones referred to the tape by an FBI undercover agent of Cherry saying he didn't mean to kill anyone and that the four dead girls "will not reproduce." In his closing argument, Jones said: "It's never too late for the truth to be told ... It's never too late for a man to be held accountable for his crimes." Jones then recited Cherry's extensive history with the Ku Klux Klan, before referring to the audio recordings presented earlier in the trial. Jones then recited the most damning statements Cherry had made in these recordings, before pointing at Cherry and stating powerfully:
"That is a confession out of this man's mouth."
Cherry was convicted of four counts of first-degree murder and sentenced to life. Bobby Frank Cherry died of cancer on November 18, 2004, at age 74, while incarcerated at the Kilby Correctional Facility.
In 1977 the Alabama Attorney General William Baxley had tried and convicted Robert "Bomber Bob" Chambliss of first degree murder. Baxley had been a student at the University of Alabama when he heard about the bombing in 1963, and later recollected: "I wanted to do something, but I didn't know what." Baxley filed murder charges against the four but the judge admitted only one defendant, Chambliss to be tried.
In 2001 and in 2002 Prosecutor Doug Jones brought to trial the cases against Thomas Edwin Blanton Jr. and Bobby Cherry who in separate trials were each convicted of four counts of murder and sentenced to life imprisonment, whereas Herman Cash, who died in 1994, was never charged with his alleged involvement in the bombing.
https://en.wikipedia.org/wiki/16th_Street_Baptist_Church_bombing
Doug Jones stands in a stark contrast to Roy Moore as much as Robert Mueller stands in contrast to Donald Trump.
The Four Spirits sculpture at Kelly Ingram Park
Lisa McNair, 53, the sister of one of the four girls, was at the Jones victory party in Birmingham, Alabama. “Oh my God, I’m so excited,” she shrieked in a phone interview as she was leaving. “For Alabama to really go anywhere Doug Jones had to win, or it was Armageddon for us, it was the end."