I agree that the defensive positioning with an infielder either right up the middle or playing shortfield in RF or LF has taken away many traditional hard ground ball or line drive singles.
Aside from hitters getting paid for the long ball, more than singles, why not upswing for the longfly than beat a shift that will rob you of previously typical hits ? Coupled with strikeout ' accumulations not seeming to matter much, no wonder they are swinging big uppercuts.