Thank you for the question.
Indeed, inequalities are reduced depending on who participates and who doesn't participate. That's it in a nutshell.
Studies show that the economic inequalities in societies in general are somewhat less pronounced in countries where this system is in place. The mechanism is that the parties and candidates speak to voters who, in other contexts, are very difficult to mobilize. The parties and candidates have an interest in reaching out to voters and talking to them.