In 2008, there was a huge economic catastrophe in the world. Some banks conspired and deliberately caused this economic disaster. This is why many people were financially disadvantaged and lost their trust in the bank. I think Satoshi made bitcoin to save people from this disaster. That is, Satoshi has created a currency where there is no third party. There will be no central bank. No one can control it. Customer to customer transactions can be done. While Bitcoin has no controller, no one will be able to intentionally disrupt its finances. Bitcoin introduced a new horizon to the world's economy and freed people from this economic catastrophe.
So I think this is why Bitcoin was created. Is that the only reason? Or are there more reasons? What is your opinion?
It might be a reason behind the creation of bitcoin but we will not know the exact reason until and unless satoshi is found and asked about it. Though it is not possible. I think, satoshi might even have created bitcoins to create a currency for anonymous peer-to-peer payments without involving any third party and that might be the reason why bitcoins are been used in most of the illegal activities carried out.
Actually speaking, i do not really think satoshi might even have considered thinking about banks before he created bitcoins. He created bitcoins to overtake banks. He might also have not thought that bitcoins will get such precious in the coming future with the huge price growth.