Sales of the Caprice, Impala SS, Buick Roadmaster, and Cadillac Fleetwood Brougham were not high enough in the '90s for GM to keep those cars going. The final assembly plant--Arlington, Texas--was designed to build over 400,000 vehicles a year, and the sales of the big cars were not high enough in those final years, to justify building them when the plant could be repurposed to build other more desirable vehicles...like pickups and SUVs.
Chrysler learned the same lesson years earlier, with the Dodge Diplomat, Plymouth Gran Fury, and Chrysler Fifth Avenue...can't be building low-production vehicle in higher-capacity factories.
And automakers make money from financing new vehicle sales. Fleet sales are almost always done on the "barrelhead"--cash or check upfront for the entire buy.