They were not cynical kissing up to previous holders of power, they were desperate attempts to cover their asses against EEOC lawsuits. And they didn't end because of Trump's second victory, they ended because the Supreme Court defanged EEOC (and half the rest of the federal regulatory agencies).

The actual reason for the "corporate DEI" in tech was that since Griggs v. Duke Power Co. (1971), EEOC could sue companies that had lower minority proportion than population norm for discrimination, and could could prove the discrimination in court using nothing but the racial makeup of the employees, and some policy at the company that could in theory have disparate impact. And under their standards, literally any policy has disparate impact.

This hit other sectors first, to which they responded by hiring more minorities. But tech had the problem that schools were consistently producing fewer minority engineering grads than the population proportion, and in a world where approximately every engineer got employed, some US tech companies would have to have lower minority representation than the population no matter what they did. And because the disparity between engineering grads and racial population proportion was so high, in fact most large companies would fail to meet the necessary minority proportions.

But EEOC would not instantly file suit against every offender, instead they would file ~40 such suits per year, targeting large companies that they considered particularly bad. And so companies that felt they might get hit soon started doing DEI programs, at first to attract more minority engineers (from other companies in the same sector, which would then fall under the limit, making it zero-sum), but then they realized that the EEOC didn't really sue the companies that were the loudest at touting their DEI credentials, and it all became extremely performative, no longer trying to attract minority talent but to be the loudest company talking about the subject. Iterate over that for a few decades and it got really weird.

It ended because Trump named 3 SC justices on his first term, and in a few important cases between 2023 and today, the new SC tore the whole thing down, and suing a company for disparate impact is now considered unconstitutional.