Simply because the law as it currently stands does not consider a marriage to a USC that did not work out as being "fraudulent", and gives the foreign national already admitted to conditional permanent residence status a "second chance" during the I-751 self-petition process to prove that the "marriage" in question was entered into "in good faith" at its inception, without having anticipated all the problems that later ensued which ultimately led to separation and divorce. That's all.
Kindly be advised that the answer above is only general in nature cannot be construed as legal advice, given that not enough facts are known. It is your responsibility to retain a lawyer to analyze the facts specific to your particular situation in order to give you specific advice. Specific answers will require cognizance of all pertinent facts about your case. Any answers offered on Avvo are of a general nature only, and are not meant to create an attorney-client relationship.
Yours is not a request for general information but invitation to a theoretical discussion on policy. This forum is not equipped for these types of discussions. Please talk to your local member of the State's Congressional delegation for that. They hold town hall meetings from time to time.
The information contained in this answer is provided for informational purposes only, and should not be construed as legal advice on any subject matter,not should it be viewed as establishing an attorney client relationship of any kind.