Shareholders put people on the board. The board hires the CEO. The CEO pushes their agenda (good or bad).

Groups like Blackrock and Vanguard get substantial shares as an organization offering retirement investments. They pool the resources of the corporate workers who are stuck with their retirement plans and the mutual fund investors whom were looking for a nestegg return when that retire. They illegally leverage this pooled investment capital to buy shares in a company of a significant percent. After gaining this leverage on a corporation, they push their board members in and they demand this agenda be implemented. The people enrolled in the retirement packages simply want to make money on investments. Nobody is investing in these packages to enable Blackrock to turn around and implement a communist agenda via DEI. The oversight organizations are already captured by cultural marxists, so they never investigate the fraud or illegal abandonment of Blackrock's fiduciary responsibility toward their retirement program investors to take actions that will be expected to guarantee a return on and protect the investors capital. Investment firms can miss a shift and make mistakes leading to losses, but to continue to push known proven bad business practices onto firms they hold stock in (on behalf of the investors) thus tanking the stocks repeatedly and predictably leading to realized losses in stock price and in earnings / profit for said company is basically not legal to knowingly do.

Because Blackrock ultimately owns everything, and whatever Blackrock says, the companies are forced to do.