Commissions don't align interests very well (real estate, cars, etc.) because you have a much greater incentive to increase your turnover and number of clients

Commissions don't align interests very well (real estate, cars, etc.) because you have a much greater incentive to increase your turnover and number of clients than to get a slightly higher price for one sale. Investment banks often have to make guarantees about selling all of the shares, and the worst thing that can happen for them is to have a broken IPO (shares close below the open price). The investment bank that led Facebook's IPO had to buy back shares immediately to prevent that from happening. Also, many of the initial shares are bought from the investment bank's book of contacts that they reached out to on their roadshow. If you lose money for your fund manager buddies, they won't invest in your next IPO.