One man is used quite commonly, even in shared use with certain freight services. SMART, if folks hadn't already noticed until now, hasn't been that "SMART" in some things, and has shown with lots of big and little issues.

A permanent two man DMU operation is more costly. Spending so much to build a line, only to run such infrequent service levers, resulting in what I would call relatively poor ridership, is a much bigger problem, from my perspective., So if you have a fixed operating budget, more bodies is more money per hour to operate, and less service hours offered.