The stock market indexes that are reported on only represent the largest corporations with monopolistic (or near) power. Much of the price rises is just more profit for these organisations. The printing of money inflates asset values, including stocks. It’s the ever increasing concentration of capital in the hands of fewer and fewer corporations as a consequence of how markets work as predicted by Marx

Why shouldnt it beat inflation?

Because the inflation that’s reported is some artificial measure of consumer prices. Asset price inflation (primarily stocks and real estate) isn’t ever discussed, but it’s also quite important.

By facilitating money to be pumped into the stock and real estate markets via structures like quantitative easing, zero interest rates, and dollars returning from being spent abroad, green line always go up.

This is of course reported as stock and real estate markets performing well, as opposed to when grocery or consumer goods prices go up which is reported as a completely unavoidable economic necessity.

This is super tldr but it’s basically Michael Hudson’s Marxian thesis on superimperialism and modern debt, if you’re interested in learning more. I can also expand on each of the points if you’re interested.

Edit: of course stock buybacks are another big part of why many stocks have performed relatively well in the last decade or so.