This is the legacy of the LaRussa-Eckersley Effect. With pitching staffs going from 10 to 12-13, the average starter just doesn't need the risk of going through the lineup 1 more time.
But there will still be elite guys like Kershaw who has averaged 6.7 innings in 11 years.
And if you look just at his peak years 2010-2016, he averaged 7 innings even.