This is an important question. There are many reason for the importance of being aware of customs and practices of other cultures. Let me name three of them.
First, we need to realize that all cultures are different. So, what is acceptable in one culture may not be acceptable in another. To be ignorant of these customs or not to care is a form of ccultural elitism, which should not be tolerated in a diverse world.
Second, without cultural sensitivity, one might be offensive. This can not only hurt on a personal level, but also hurt a business deal. For example, to show disrespect, especially to an older person, in an Asian culture can totally turn a deal sour. And I am sure that many deals were broken up on account of this and other cultural offenses.
Third, when there is cultural sensitivity, there is also trust. When there is trust, there is a better basis for business. Hence, there is no reason to neglect the customs of others.