One of the reasons of this is the inflation: it is a kind of regressive tax, this tax is paid mostly by the poor because they loose their savings, while the wealthy keep their savings not in money but in assets.
Isn't the reason that rich people invest in various assets simply because they have enough money for their daily lives and can afford other ways of investing? 
Give a poor person bitcoins or other assets, and the first thing he will do with them is sell them. And I don't think we need to condemn him for this, because firstly we need to ensure that basic needs are met, and then we need to think about investments. Moreover, Nvidia shares or cryptocurrency cannot be used to pay for utilities, for example.
But those who have suitable standard of living have more liberty to long term investment and shares holding than someone living below the basic necessity.