Carlin quit because he had committed IMHO fraud upon the FISA Court and Admniral Rogers called him on it.
Based on a time line I have seen, Carlin submitted the material for the Carter Page Warrant at the same time he had a report from Rogers that Carlin was required to submit to the FISA Court regarding activities of those accessing NSA Databases.
That report was in direct violation of the FISA COURT Judges orders as to access and searching means/methods by Contractors.
Carlin sat on that information until AFTER the court approved the Warrant. Later that day he then submitted the report.
If history records events accurately Admiral Rogers will be known as the guy who helped save the Republic.