Someday it will happen. Bethesda filled a patent last year for a Fallout series.
Here's is the actual patent: http://tsdr.uspto.gov/documentviewer?caseId=sn85818163&docId=APP20130111071552#docIndex=13&page=1
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Or they filed a patent on it so if anyone made a tv series of it they could sue. Most patents that go through are used for that purpose.