One part of it was tennis was slower, evidently so, in the wooden era.
But the other part was Graf was not a great anticipator. I did another thread about how she frequently got caught flat footed just running from the center mark to the forehand corner because she was leaning towards moving to the backhand corner (and run around) all the time and didn't anticipate soon enough to correct. When you take a bit longer to identify where you need to be, you are going to fidget with small steps.
Look at 7:53. Terrible footwork. Waited way too long to decide to move up the court for a short ball and then didn't just use two-three hop steps to get there with momentum and instead took several smaller steps and ended up overplaying the shot.
There is no player, on either tour, whose game is so mythologized and whose flaws are as glossed over as Graf.