The work of investment bankers are not the simple. Bankers sell companies and get paid through commission. The larger they sell, the more they get. Another thing why average banker earns a lot is because of the margin. They handle a lot of money all the time. The only expense bankers handle is their office. Other expenses are insignificant compared to the multi dollar fee they charge. In short, investment bankers earn a lot of money because of hefty commissions but no expenses.
For private equity and hedge fund, they also make a lot of money. The difference is that they get other income called carry which is return of investments. For funds that do well, this creates huge wealth. There are small numbers of people who can get into the industry. Getting an investment banking job is rather difficult. This is because they limit people who break in and raise money out of it. Being an investment banker is a good idea especially if you want to earn huge amount of money. It is pretty lucrative industry that you should get into.