Why don’t “big brands” just build their own "branded community websites” for their customers & followers?

I think there are many reasons for doing so:

1- It's a burden: It's true that the technology is available. However, the platform needs to be built and developed. It's quality needs to be tested. It needs to be marketed and gain public awareness. it needs to be provided with maintenance and continuous improvement, and many other processes. Social media websites work day and night to keep their platforms going.2- After all this hard work, the platform won't reach the same level of quality. People who work in social media websites are more specialized, experienced, and professional. They have developed their own database and lessons learned throughout the years. All of this ensures providing the best user experience possible.3- Social media websites have a larger audience. They are more widely spread. They already have reached masses. It would be unwise to ignore the audience on Facebook for example and build your own platform.4- Change resistance: People fear change it's a known fact. This simply will limit the potentials of the platform immensely. To sum up, why waist effort, time, and money for a low quality platform withal high risk of failure? That been said, many brands provide blogs, forums, live chat customer service, mobile applications, and other ways for reaching their potential customers.

I do agree with Gadheer & Walid 's statements, but would like to share another aspect of big brands.

Mr. Khatim, do you think, that big brands, do use their consumers as their media to advertise ? I do look they use. They do not use the social media to advertise but they use the users of social media as a mass advertising tool.

Now, on front end, they are already recognized enough that advertisement media apporach to them to offer advertisements on their respected medias. The need to apporach to any agency.

because they depend on the main social media as they cannot compete them, also all ppl using it also all profisional using it so the easy way is to use social media as marketing and follow up