Efficiency is more a side effect of the profit motive, but it's not the driving force nor is it a justification.
Capitalism at its very core is meant to produce as much as possible (aka, profit), and to allow that production to continuously grow (return on investment). Technological efficiency as a tool enables the same production with less resources- but if you already have those resources, why not use more resources to increase production exponentially and get the most profit?
This results in the Jevons Paradox. Efficiency is great, but regardless of how efficiently we use resources, capitalism will grow to fill its container and eventually burst it.