A new pro gets a 2 year contract. If they do not perform and get results they are dropped and out of a job. Invariably they have given up on education without qualifications so will have problems getting a decent job and no doubt have spent many years of hard effort (by themselves and family) to get to that point. So the pressure on them to perform is tremendous. Therefore drugs in cycling is hardly surprising.
Also we, as fans, want to see long mountain stages with several climbs and 'super human' rides. That is not possible for mere humans. If we were more realistic and had less severe, shorter stages at slower speeds would it still have the same spectator appeal?