1. A union purports to represent the interests of a labor force to its management. Those interests are diverse, because the workplace is diverse, but the issues with largest intersection tend to be compensation, time off, and health benefits.
2. In the past several years, there has been an unambiguous inclination for the stultifying, puritanical, logocentric manner of leftist political spaces to also invade and supplant workplace norms and office culture. This goes as far back as Brandon Eich being ousted for making a donation that follows his conscience, but also includes a funded menstrual app startup that has to claim to serve not women, but "people with periods". It's an insane worldview that maybe 5% of Americans agree with, yet it's the dominant corporate culture.
3. These supposedly moral issues (I called them fashions) being broadly unpopular are nonetheless enforced norms. The way they are enforced is through the actions of HR departments, and particularly on the backs of legal theories such as disparate impact and workplace fairness.
4. Unions, i.e. labor relations, are exactly the type of concern that would fall under (3) and therefore susceptible to becoming another vector for propagating (2). That, along with the fact that most Google employees are extremely well compensated, make it reasonable that progress on (1) is not nearly the likely outcome of a union, while (2) is an easily foreseeable side effect, intended or otherwise.
5. Again, evidence of how unions in other knowledge work fields such as journalism, supports this. Journalists have been outed from their positions, without support from their unions, for expressing basic journalistic freedoms. Isn't the union supposed to protect you from being fired for doing your job? Education is another such field where we can see plainly what's happening.
Lastly, anti-racism is a moral abomination under its current critical theory construction popularized by e.g. Kendi, DiAngelo etc. Also, it's not the union's job to propagate morals or enforce them onto labor.