A businessperson may wish to efficiently provide needed goods to people and to donate lots of money to charity. That's conventionally considered a good motive. On the other hand, someone could go into politics purely to gain prestige and power. That might be thought of as a bad motive. The naivet of that assumption should be obvious.
People are people.
They don't become saints when they choose government work. It does no good to argue that people can make more money in business than in politics. First, it's not true for everyone. Second, people seek more in life than money. For some, power and the prestige issuing from the mystique of the state outweighs the money forgone.