This to me kind of highlights the disconnect of unions in software engineering. In many companies including Google, there are parallel IC and management tracks. There are ICs in leadership positions but just without any reports. Does that mean, e.g. an L7 staff engineer can unionize but not an L5 manager?
And then it leads to me wonder, why can't managers unionize in a typical union? Even at a big old-fashioned manufacturing company with a union, the managers are still individual people who are separate from the company itself. Presumably the reason is that they already have better conditions, they're highly paid, maybe they're already aligned with company itself because they have an ownership stake or some incentive bonus structure. All of those arguments apply to software engineers as well.
This may be a cheesy analogy, but in some ways all software engineers in tech are already effectively the middle managers. They oversee the "assembly line" that generates the revenue for the business, which just happens to be software rather than people.