Why a major leaguer doesn't hustle on routine infield ground balls (or pop flies) because the odds of their being an error is less than 1 in 100. Why risk an injury or waste energy that may be needed later?
Perfect pitches go by major league hitters, sometimes, because major league pitchers fooled them.
I think you've nailed the reasons. They don't hustle in situations where it rarely matters.
As far as watching perfect pitchers, to them, it wasn't perfect. They were guessing something else. MLB batters are striking out about 1 in 5 AB nowadays. When the pitchers are that good (I know some would say the hitters are just that bad), you're going to start guessing and you're going to get fooled.