People usually invest in producing some thing. In order for that thing to have value, you need people who spend to buy it. It seems pretty simple to me. As for

People usually invest in producing some thing. In order for that thing to have value, you need people who spend to buy it. It seems pretty simple to me. As for why it might be better to give money to someone to spend than to someone who invests: someone who can't afford to spend needs money more than someone who can afford to invest.