I am wondering, for example, why do we think that maximum efficiency is a social good?
We don't. Sometimes such privileging leads to outcomes that are socially, at least to philosophers, probably bad. Consider a city investment policy common in the United States: tax breaks are given to entice developers to build condominiums that only a small percentage of wage earners in City X can afford to live in. Tax revenues may go up in the short-term, but property taxes go up too, forcing a fair percentage of local residents to move out, to lower cost housing. Although the developers and local politicians may see a win for increasing tax revenues, they are ignoring the greater social good that might occur if all wage earners who desire to live in Neighborhood Y in City X could in fact afford to live there. Assume these hypothetical low(er) wage earners mostly work in Neighborhood Y, and the new condominium owners mostly live and work in Neighborhood Y as well. We then see where strange places like Naples, Florida come from, where a huge percentage of service-industry wage earners live outside city limits because low cost housing is quite rare. These sure seems undesirable in the long term.