As per me
THE FIRST REASON IS: Boredom
The format of the show does not change much. A small skit is usually performed by the characters with Sidhu Paaji giving his own commentary and shayari. Whether it's Kapil bickering with his onscreen wife Sumona or having the famous verbal fight with Palak (Kiku Sharda) or bua trying to woo the guests on the show, monotony has certainly set in with nothing fresh to offer. The only constant change is the guests who come on the show, though some have come more than once also. This could be another reason why the channel and makers are said to be taking a break and will be seen after a short hiatus to make the show more innovative and interesting.
THE SECOND REASON IS: Shelf life
Take the most popular fiction and nonfiction shows on Indian Television, one day, they all have to come to an end. When a show reaches its peak, its difficult to sustain it and retain the audiences' attention. From Uttaran to Kyunki Saas Bhi Bahu Thi, every show, be it reality or fiction has a shelf life. Comedy Nights with Kapil is no exception. The format has perhaps offered everything it could and the innovative factor about the show is slowly dying. Though it remains hugely popular and unbeaten, it cannot entertain beyond a certain point. And maybe this is one reason why the channel and makers are taking a break to bring in new concepts and perhaps new characters.
But the real reason can be very different as channel has introduced "Comedy Night Live" so real reason could be business fight between channel and production.