What is the market? The market is something like the returns of the S&P 500 index. How do we get the returns of the market? Make a fund that tracks the S&P 500 index. Why do we have funds that use market-cap weightings? Because we want to track the market.
I guess it's not about having an equal representation of companies or industries or sectors, it's about having an equal representation of where dollars are allocated. The goal isn't to take a dollar and buy a share of each company, the goal is to take a dollar and buy more of the companies that other people own more of and less of the ones they don't?
My point is market-cap weighted index funds are an investment strategy and not some neutral default thing that people seem to think they are (or maybe I'm projecting).