There are a couple reasons. When poor people get money they spend it, and when rich people get money they invest it. The former promotes healthy economic activity while the latter ties up wealth in speculative bubbles like Bitcoin, real estate, art, etc. Henry Ford, for all his faults, understood the importance of paying his employees enough to buy his cars. Today's wealthy are so consumed by greed that they are undermining the social fabric on which their wealth depends.
And many of them do accept welfare that dwarfs social services through juicy subsidies and regulatory capture. What is the military industrial complex after all than welfare for weapons manufacturers?
I'm not sure you know what "investing" means.
Investing creates capital for businesses to operate and expand. That pays for labor, employee benefits, taxes (ever hear of the higher capital gains tax rate?), and so on. Businesses operate on revenue to a fixed level. Infusions of capital allow for expansion, which means more jobs/better jobs for the workers.
The so-called "greed" of the wealthy is what drives economic growth just as much as employees spending and consuming. What does kill growth is more government programs. Government is a consumer of wealth. Gov't produces nothing and adds zero to the GDP. When Gov't gets $1 from "the wealthy", it distributes less than that to the beneficiaries.
Capital drives capitalism. Without the entrepreneurs and investors, there would be no Ford, GM, GE, Amazon, Google, Starbucks, Taco Bell, Apple and other large, nationwide companies to pay good wages and benefits.
As for being able to buy what you help make, that's not an income issue. It's a tax issue. My last calculation said roughly 50% of my income goes to taxes at some level -- income taxes for state and federal, Social Security, Medicare, State Health Insurance for uninsured, sales/excise, gasoline, roads, and pretty much any fees I pay to register vehicles, bikes, pets, etc, etc. As consumption and taxes have risen, so has the need for more household income. The US used to allow for a single wage earner to pay for a family's expenses, save for a home, take care of medical expenses, etc. Few owned cars, and "essentials" like TVs, cable service, internet access, cell phones, computers, tablets, and such didn't exist. We are a services-oriented, consumer driven economy now.
Back then, the economy was dependent on manufacturing mostly. Trump is returning some of those manufacturing jobs. November saw the largest number of new manufacturing jobs created in US history.
So, yes, investing is for people with money they can afford to invest. Maybe instead of giving the rest of the people more and more of the investor's income, let's try and help more people get to a point where they HAVE money to invest?