His old persona is presumably the property of Comedy Central and it’s not really suitable for late-night television anyway (too political). Assuming that Colbert has any other settings or styles, any variant from them will get panned by people who actually want to know that the old persona is on the Late Show*. What is left for Stephen Colbert to bring to the table?
I ask out of only mild interest: I don’t watch television. Not out of snobbery; my wife doesn’t want to shell out the money for cable, and I don’t care enough to push back on it.
*Although they wouldn’t watch it, which is the basic problem right there.