SM isn't always easier.
SM is fairly modular.
SM isn't any cheaper when compared to BM doubles in doing double-tank dives. If you want to bring in up singletank dives into the equation, and you're going to be using the same tanks as you were for double-tank diving, then maybe you have a point.
There would still be adjustments to be made to the SM tanks, whether you use cambands or hose clamps, they'll still be there and attachment points(bolt snaps or worse caribiners or butterfly clips) will still be loose - this may introduce danglies and snag points to a recreational setup. Then you'd still have to rearrange your hoses.
Point being, SM tanks/regulators still require adjustment to be used properly as a recreational single tank setup. Going through that work costs time(and money?), just like breaking apart doubles.
There's no need to stretch out for an excuse to make SM cheaper. Modular isn't always cheaper, it could be argued that BM doubles are just as modular.