to add to what I said earlier I think another reason why doctors prescribe so much at first is to increase the blocking effect, as well as keep your tolerance high to decrease side effects such as drowsiness and feeling high. It could also be because doctors have never taken suboxone and are going on patient feedback. most suboxone patients are quite experienced with drug seeking behavious, so if the doctor is willing to write a script for 16, 24, even 32 mg they're likely to oblige him.
another factor is a little less honest, they are looking for franchise clients and the more they prescribe the longer people will be on it, not to mention any back dealinkgs with the pharm company (kick backs, etc).