It has everything to do with expectations! If everyone around you bottle feeds, you're more likely to bottle feed. Ditto breast feeding. In any case for pumping you need more than just the pump: you need the bottles, the sterilising kit, the storage space both at work and at home. Choice is a red herring. People can be and are pressured into making particular choices, and people's choices are influenced by the information they have available. Not everyone will conform to societal expectations, for sure, but the change in choices when those expectations change does suggest that they are hugely influential.