At that time, the 737 MAX was just entering service. There was, of course, no hint of any turbulence on the horizon.
The business case for the New Midmarket Aircraft was difficult even then. So why not look at a 767RE and restarting the 757 line, also up upgrades?
Boeing being Boeing, it looks at everything. It ruled out restarting the 757 line (the challenges would have been pretty daunting).
The 767 got more studious traction, including simply restarting the passenger line and providing a really cheap acquisition. A 767RE, however, was viewed as too complex under the circumstances and it would compete with the 787.
American Airlines and United Airlines were actually interested in the airplane restart.
B767F-RE may be to counter A330-900F approach to a major cargo airline.
B767P-RE likely would be met favorably--by Airbus.