I’m not sure there ever was such a time - at least, a time when small shareholders in large, publicly traded companies with a diverse shareholder base had any meaningful role in corporate governance. Econ 101 dealt with “Theory of the Firm” problems of collective action and agency costs and aligning shareholder/management interests back when I took Econ 101…which was a very long time ago, long predating high-speed trading and ETF’s eating the shareholder ecosystem.
Plus…I’m not sure that the problems discussed in this thread are all the same problem, or at all related to to each other. High-speed traders make up a huge amount of the trades in equity markets these days, but they don’t have that big a share of the ownership of the market. Big index funds and ETF’s and other passive investment vehicles do have a big share - but even though the investors and managers are passive in their holdings, those shares still get voted. BlackRock and Fidelity - and the duopoly of ISS and Glass Lewis - very much do pay attention to issues of corporate governance and very much make themselves known to the BOD and C-suite folks (which is why Elon complains about ISS and Glass Lewis from time to time).
I mean, these things can have an effect on corporate management. If a huge portion of each company in a sector is owned by “universal investors,” who all own huge portions in every company in the sector, then the investors (and then possibly the managers) don’t care that much about whether individual firms in the sector perform well or poorly relatively to each other. Or in collecting information about which firm is likely to succeed or not. Or in having those firms compete against each other. If 90% of each company in a sector was owned by a single index fund, you end up with an effective monopoly - not by firms, but by the ownership of each firm.
But I’m not sure it’s true that less attention is being paid to the companies by the investors collectively - it’s just that the attention is being paid by the large fund asset managers and the proxy advisors on behalf of the beneficial owners, rather than individual investors.