Well, any number of historical reasons: slavery; violence against indigenous people; colonial sources, such as exporting of natural resources; the actions of a state, which might not be recognised as an authority; or simply inherited property from a time of aristocracy.
Equally, people might reject systems of ownership out of hand, and consider the gulf of wealth causes by those systems to be the product of immoral behaviour.
Equally, people might reject systems of ownership out of hand, and consider the gulf of wealth causes by those systems to be the product of immoral behaviour.