It ' s the same reason why many corporations own multiple brands that offer the same product or service 1 . To attract different target groups via marketing and branding 2 . To ward off competitors by providing inhouse alternatives if there are no objective differences between products , consumers might distribute equally between brands , by offering multiple brands you consolidate more of the market simply by owning alternatives 3 . To avoid costly change after acquisitions e . g . some of these sites started of independently and then got bought , consolidation would be costly and offer no gain 4 . Reach competing B 2 B customers e . g . some ad buyers might want exclusivity on a site , which they can offer as they larger network always has an alternative site for a competitor 5 . Reap tax benefits and leverage tax loopholesand my favorite factor in all business decisions 6 Just cause , as the management really hasn ' t though about this and just keeps statusquo .