It's a multitude of factors IMO. I think the size of the playing fields likely plateaued about a decade ago, so I'm not sure how much of a factor that still is. But yes, a larger field = more luck is needed to make a final table.
Also, many old school pros still haven't fully adapted to new school styles of play. From what I've heard Hellmuth is a good example of this. He is an excellent tournament player, but doesn't fare so well at cash games, with his antiquated style of play often cited as the reason.
In addition, it would seem that the super-aggressive style of many newer players does lend itself to luck being more of a factor in bigger pots. I mean, even if you're 60-40 to win the pot, how many all-ins are you going to win if you keep calling those? Theoretically in the long, you still should come out ahead. But on any given night, they can wipe your stack out pretty easy. Those players tend to make their money off (1) people folding when they've already invested something in the pot, (2) falling ass backwards into big hands when they play rags, and (3) winning as the underdog when get called, IMO.
