This might seem calculating and cold, but that's basically how government agencies work. It doesn't make sense to spend unlimited amounts of money to save a life, so government agencies have some sort of a dollar value on a life[1], above which where they won't bother doing interventions. For instance if it takes $15M to save a life, and that's above the DoT's estimate of $12.5M, then they won't bother. That's not to say that Boeing is in the right here, but if they were in the wrong it's not because "If X is less than the cost of a recall, we don't do one", it's because they grossly undervalued a life in their calculations.
[1] https://en.wikipedia.org/wiki/Value_of_life#United_States