I agree with you, Bill.  Although there are definitely fewer priests than there were say, in the 50's or 60's, the reduced number of priests is not the "one root cause" of the decline of parishes.  Far fewer people choose to remain in the Church.  It seems to me that the fundamental reason is that the Church chose not to renew itself through Vatican 2.  Even the changes that did occur in the Church were all handed down from the top.  And the backpedaling and, later the backlash, started very quickly, re-consolidating the monarchical model.    As you say, people, in ever greater numbers, are not longer "buying what the Church is selling".