I would have to imagine that all four bidders presented plans with varying risk and cost which meet the requirements. Since NASA had a mandate to pick multiple

I would have to imagine that all four bidders presented plans with varying risk and cost which meet the requirements. Since NASA had a mandate to pick multiple winners there were probably two winning strategies, be low cost or be low risk. I's speculate that Boeing presented the low risk route--nobody doubts they can meet the requirement if they get paid enough. I'd imagine that SpaceX presented the lost cost bid, probably viewing their bid as more of a subsidy for work and risks they are undertaking regardless.