I seem to remember the late Fr. Andrew Greeley, who described himself as a "statistical sociologist" in one of his books making exactly this point.  In fact, I recall that he said that the  bishops did this once, learned that most people in the pews thought sermons were poor, that church hierarchy were uninterested in them, and were generally lowly regarded.  But they liked "being Catholics".   The bishops never again sought out the PEW surveys for such opinions.   Easier and safer to just ask a selected group.  The fact that the hierarchy has shown no interest in finding out why people leave has been dealt with on this site specifically before.