It is normal nowadays that idols participate in the TV shows such as We Got Married and pretend to be a couple. But actually there are ‘couples’ in the group as well.
Probably this is not popular now, 8 or 9 years ago this ‘idol couple’ is really popular. The special thing of this kind of couple is that couples consist of boys.
The Japanese and Korean music industry actively encourages bromance among male celebrities (particularly members of boy bands) as part of the fan service to please the audience. (wikipedia)
They are not really dating and they are just colleagues or friends but this ‘couple’ makes fans have more topics. Normally the group can get more fans if they are attractive.
One of the most popular CPs was Heechul and Han Geng. Even though Han Geng has already come back to China and has his career in China, this CP is still remembered by many people.