Competitors have a hard time getting off the ground because the dominant player is promoting its own products. Classic monopoly. Competition won't be good if nobody uses them.

Google maps might be a good example, MapQuest and Terraserver used to be better for navigation and satellite photos. Did they fail because of business reasons or self promotion? Hard to know, but Google pulled the same shit as MS got antitrust for. Bundling their own maps app pre-installed on their dominant mobile OS