I believe it is because the word "renowned" also implies a notion of respect that the word "well-known" doesn't. In other words, renowned means famous AND respected and well-known just means famous. I hope that helps.

To be honest, there is not much difference between famous, well-known or renowned. There is the sense of honour with renowned, but I doubt if many people either know or use that distinction. The difference in your piece seems somewhat arbitrary, because some TV personalities have renown.