Morikawa, who became the first American to win the DP World Tour's season-ending showpiece in Dubai last year, took to social media to explain the reason for his absence, citing "upcoming personal commitments."
The two-time major winner's withdrawal means the DP World Tour Championship's record of not having a repeat winner since its inception in 2009 will continue for at least one more year.
Morikawa qualified for the DP World Tour's season finale largely by virtue of his top-five finishes at the Masters and US Open. He made eight starts in qualifying tournaments, including two DP World Tour events in the Middle East in January, though he was only 35th out of 50 in the season-long points list.
Another American, Will Zalatoris, also won't be in attendance as he continues his recovery from a back injury. The 26-year-old was ranked sixth on the points list.
Headlining this week's event is FedEx Cup champion Rory McIlroy, who also sits atop the points list entering the finale.
McIlroy is gunning for a fourth Race to Dubai title, having previously captured the Order of Merit title in 2012, 2014, 2015.
The Northern Irishman's closest rivals on the points list are Ryan Fox, Matt Fitzpatrick, Tommy Fleetwood and Viktor Hovland.