Advancing to title games was just a touch easier back then.
I wonder if that is the case.
There are two title game participants when the field is 8 teams, and there are two title game participants when the field is 66 teams. "Title game appearances" haven't become any scarcer: there remain two per year. The difficulty in moving up the bracket by winning (in larger fields) contrasts with the difficulty of being left out entirely (in smaller fields).
Consider BCS era vs 4-team playoff, which is fresh in everyone's memory. Which is harder: (a) finishing the regular season in top two; or (b) finishing regular season in the top four and winning one game? The former would get you to the title game in the BCS era; the latter would get you to the title game now. To me, it's a wash: you're roughly twice as likely to make a twice-as-big field, but then roughly half as likely to win the tourney once in, which balances out.