Its that bias that is as big a factor to sales as anything else. It allows the manufacturers to hitch onto a franchise's name value, and generate buzz.
Part of the reason why new IPs have a hard time to get a foothold initially. Lesser informed consumers will see a new title, and will wait to pull the trigger until they see a review. They see "Random Title 5" and will more likely buy it blindly because it's assumed to have been refined and improved upon for 4 titles.