According to a Suzuki spokesperson, the main issue came down to floorspace. Suzuki hoped to move to a bigger display for the 2009 show, which would have allowed for larger "active" displays.
Space constraints of the Detroit show's venue - Cobo Hall - have been a long-running complaint of exhibitors. Multiple plans to expand Cobo's show floor have been proposed by Michigan politicians over the last year; to date, none have been approved.
Suzuki is the third major automaker to pull out of the show, following Isuzu in 2005 and Porsche in 2007. Although Porsche's withdrawal stemmed from lagging sales in Michigan, Isuzu also cited space restrictions as a factor in leaving.
Source: Detroit News