They did trickle down, to the highest valuations of companies, leading edge technology, and high stock prices.
If you're a middle class american without a brokerage / investment account. You are getting shafted.
Immigrants in the USA are especially risk averse when it comes to investing in the stock market, because the countries they come from are corrupt and they have been screwed in the past. It's amazing how many Americans with the means to invest in the market, would rather eat out every day, buy a new car and iphone every 1-2 years, drown in debt, and fail to reap the rewards of capitalism. Not investing in companies through the stock market is the very definition of not taking advantage of the capitalistic society we live in.
K-12 education in the US should have a mandatory course on the financial market and educate people about the tax advantaged accounts available to them. Of course, this is like the government pouring gasoline on its own fire, so it will never happen. Why? Because the govt has no incentive to help you reduce your tax burden, while reducing their tax revenue.
People don't have a clue about 401k, HSA, Roth IRA, Back-door Roth IRA, 529 college savings accounts, student interest deductions, brokerage accounts and capital gains tax, and the advantages of each.
Credit is horrible to the financially illiterate consumer, but is empowering to those that understand economics and capitalism, avoid consumerism, and understand how to invest capital and make a return.