Why might network externalities cause a new cable provider to be unsuccessful when it tries to enter the market?

One reason a new cable company may be unsuccessful when entering the market is if they charge too much for installation. Established companies are usually able to offer free installation. Another problem arises when the new cable company has a different channel lineup than other companies already in the area. Most people don't want to give up channels they are used to having, especially if one of those channels shows a current popular show.