Well the main goal of flipping is so that NOBODY KNOWS ABOUT IT! If you started interviewing ppl beforehand, word would get out an it would no longer be a secret. Worst yet, another station could catch wind of it and flip to CHR BEFOREhand. Then you'd be in 'sloppy 2nds'. They must keep it secret from everyone as long as possible.
We've already seen cases where even rumors of a flip leak out an ppl start buying up domain names (.com) to attempt to resell it or hold it hostage from the flipee. and thats just an example of 1 reprecusion.