In short, most of them don't have the capability to invest as they are just living from paycheck to paycheck. Only those who have excess can have the option to invest, hence, most people in the poor category don't have the mindset to set aside funds because they are barely surviving. And with such capability, some of them are trying their luck in gambling, for the main reason that they are trying to hit their luck. And also, it will only require small amount of money to enter in this game.
And on the other hand in most cases yes as you said that poor people prefer everything that is instant in terms of producing, the financial situation and circumstances are one of the factors that encourage them to get instant results where simply they think that by winning in gambling then it will be able to help them to ease the burden of their lives, but however yes of course that is the wrong mindset. So I think that poor people should not be involved in these two activities, namely investment and gambling.