CNN  —  From the outside, the idea made no sense at all. Why would a broadcast network cancel one of its best-known shows that ranks number one in its time slot? But on the inside, at CBS, there were several plausible answers to that question. While “The Late Show” host Stephen Colbert was on his usual mid-summer vacation earlier this month, CBS executives weighed the pros and cons of canceling the unique but unfortunately unprofitable show. The “cons” were obvious, as evidenced by the studio