Originally Posted by Mustard
It has nothing to do with the depth of the field, but to do with the number of hardcourts on tour today, and also the more power elements in the modern game.
The power game and hc are part of it, but the greater depth influence great players to retire early. No one likes to flame out in early round. Sampras retire early despite winning the 02 USO, because he kept on losing and his ranking plummeted. This isn't Bjorkman or Santoro, the journeyman use to get flamed out early, so they pursue to have a long career. For legendary player, he doesn't like to stick around. If Federer isn't part of a the elite 4, and his ranking fell off the chart, that increases his chance to retire. Even Roddick retire at 30 because the depth of the field left him zero chance to winning anything.
Tier1(goat): Federer; Tier 1.5: Laver, Gonzales, Sampras, Nadal, Borg;
Tier 2: Lendl, Connors, Rosewall, Tilden; Tier 2.5: McEnroe, Agassi