I mean, they're ultimately trying to maximize TV revenue but the rankings have generally been fair in terms of who's top 5, 10, etc. I think when you're looking at the current system you could make the argument in a lot of cases that #4 has a reasonable chance of winning the whole thing. But, in a different system, #8 is surely far more of a stretch, especially since now there's 3 games to be played and they'll be seeded against the top. 8 team playoff is really a way to include #5 and 6, who have a fringe chance of winning the title, and keep things more fair with no byes or wild cards. #7 and 8 in most years will have virtually 0 chance of winning, since it's not a linear relationship in the rankings, more logarithmic (some people assume that team ranked #2 is equidistant from #1 and #3 but that is very obviously not the case in most years, usually looks more like 1...2.....3......4............5, or maybe 1..2..............3.4..5, you get the picture, point being the gap between #8 and #1 is usually significantly more than 2x the gap from #4 to #1.