The growth of passive investing is not limited to the ETF wrapper. Other indexing investment products have also been growing, with mutual funds dominating. Vanguard has pushed the industry towards such investment products with low expense ratios. Vanguard boasts an average expense ratio of 19bps compared to an industry average of 108bps. Robinhood has pushed the industry to commission-free trading. Most large asset managers have currently, significant platforms with commission-free trading investment products (from Fidelity, Vanguard, Charles Schwab).
Customers — Investors should be extremely happy with all these developments. However, there is one major concern whose ugly head may not be noticeable. An elephant is in the room, here too. Its name is `The Big Three`. The concentration power of three US-based companies, Blackrock, Vanguard, and State Street, and its ramifications has gone largely unnoticed.
Blackrock passed the $7 trillion AUM by the end of 2019. A y-on-y increase of $1.5trillion.
Vanguard passed the $6 trillion AUM and State Street the $3trillion AUM.
These three corporates manage $16 trillion AUM. This is a 45% increase from 2017 ($11 trillion AUM)!
Through a visualization produced by Corpnet Research what becomes clear is that `The Big Three` are the largest shareholders in 40% of all publicly traded stocks in the US 
The growth of low-cost investing, the disruption of the brokerage business model and the digitalization of the investment process, has created this excessive concentration in the Big Three asset managers.
Blackrock, Vanguard, and State Street have corporate control over 40% of the US stock market! These giant index fund businesses have too much shareholder voting power. That is one of the reasons that it matters a lot what the Fink says about climate change and ESG. In this case, we like his commitment but let’s be aware of this Corporate Governance entity in the room