Well people scam because they don't have enough or not contented with what they have in other word being criminal minded could be another major factor that may lead people to scam other people.
I think people scam because they have the addiction to do so. They feel excitement and happiness while scamming. Innocent people are the easiest prey for these scammers. I think scammers are not able to earn money with legal means and they think that legal earnings are very little and also hard work and the easy way to make money for them is to scam so, that's why they do that.
Some people used to scam because they are not having any kind of feeling they just want to increase the money and the wealth they are not having any concern with the humanity so it is the best timed buy the bitcoin and to hold till the price of the bitcoin will increase instead of the losing the money of the other people and giving them the chance to have the loss of bitcoin by the scamming.