You think they are cherry picking? For what reason? It's not that serious. They don't give their criteria, and each source might have had somewhat different criteria. But, any list from America is going to have a lot of the same shows.
Greatest is not best. The TV guide is ranking greatest, which would weigh things like cultural impact, ratings dominance, etc. Greatness is resume. Best, in this case, is just a measure of how much you enjoy it. It appears that Greatest and best are synonyms in this list.
Like look at Kareem. Maybe greatest basketball player of all time. Not the best tho. I'm picking a lot of guys over him who I think are better players. He was the best at his time, tho. Just like a lot of these old TV shows.
Bill Walton is like the miniseries on the list. Somewhere near top 5 best but nowhere near top 5 greatest