Why do websites use different URLS for mobile and desktop

[razasaeed]

Although Google and Bing have recommended that the same URL be used for serving desktop and mobile websites, portals like airbnb are using different URLS to serve mobile and web users.

Does anyone know why this is being done even though it is not GOOD for SEO?

[Sarbs]

Its often a case of logistics in updating a site to be responsive design, the only way the same URL can serve dynamic content to mobile and desktop devices. Previously many sites have had to create alternate mobile sites.

So while responsive is now the recomended approach, many sites still use subdomains or directorys. This useful post also casts light on when these multiple methods are most suitable. When Responsive Design is not an option.

Hope this helps.

[David_ODonnell]

Some sites serve different content to mobile devices, therefore require a seperate URL.

Google and Bing currently prefer responsive design because it allows the same URL to be displayed on desktop and mobile devices and requires less crawling ./ indexing on their behalf.