Answer by Jane Chin, Founder and President of Medical Science Liaison Institute (2004-present):
I'll answer both your original question (why successful people are arrogant) and the clarifying question (what's the cost of being nice) because they are related in terms of the assumption behind the question.
The sequence is as follows:
Most successful people started out like most ordinary people. Most of them do not act arrogantly, and many are probably "nice by default". You go about your day, making your bed (or not), getting along with people (or not), and generally go with the flow of society (or your particular social bubble).
One day, or overnight, or after you've been bought out by the mothership of your industry and your net worth inflates exponentially to the point where it's easier to explain your net worth by using exponential factors of 10 ... success has happened to you!
You don't see it at first, but soon you start noticing that a large number of people start to want something from you: your contacts, your money, your time, your attention, your advice, your endorsements or recommendations. Some people you don't even equate as acquaintances start dropping your name for their own gain. What hurts the most is that some who you thought were your friends - even relatives - show you their true faces, and frankly, they don't look so nice or decent.
You try to be polite at the beginning. Your mum taught you manners, and you are generally a decent human being. But your patience starts to wear thin day after day after day of the same "Gimme! Gimme! Gimme!"
Until one day you decide that in order for you to remain productive and effective and otherwise sane as a human being carrying about your business, you need to create some type of a protective bubble around yourself.
You don't smile as much as you used to. You are more cautious about how you respond to people who approach you, lest they should interpret your courtesy as receptiveness and it's back to "Gimme! Gimme! Gimme!" all over again. In some cases, your goodwill has been worn down to the point where you are quick to yell at Jane Doe today because of something idiotic that John Doe had done to you yesterday.
You feel sorry about that, and you feel bad about some of little hurts and slights you've given in your desire for self-preservation, but you had to move on. You no longer have the luxury of contemplating the social nuances of interpersonal relationships when mothership expects its ROI from your IPO.
Hence, successful people often come across as arrogant, either by design or by nurture (occasionally by nature, yes), because they tend to attract a swarm of followers, admirers, curious onlookers, critics, stalkers, and a diversity of people that less-than-successful people don't tend to attract. Their arrogance is the shell they use to protect themselves, and 99% of the time, it's not personal.