AWU is not a traditional workers' union. It is a political advocacy organization. AWU's mission statement is explicitly and emphatically not to further full-time employee's interests. Rather, it is organized primarily as a vehicle for achieving a broader political end ("social justice", as that term is construed by AWU's organizers), potentially at employees' expense. Almost none of AWU's projects have focused on Googlers' work conditions or pay. Instead, they have focused nearly exclusively on modifying Google's products and policing its contracts, often in ways I find extremely objectionable. For example, they have lobbied heavily for Google to increase censorship of YouTube and Search, and to demonetize "problematic" content creators. They consistently advocate increasing institutional support for DEI efforts, and it was their efforts which led to the creation of Alphabet's Chief Diversity Officer position. They agitated on behalf of ex-employee Timnit Gebru against Google's ML work, which is obviously a threat to the hundreds of Google workers whose jobs depend on the models that Gebru's research criticized. Why should ordinary Google workers support such a "union"?
I want to add that I agree with some of AWU political stands. For example, they opposed Project Dragonfly, a censored version of Google Search intended for the Chinese market. They opposed Google contracts with the DoD and CPB. I think these are all worthy causes and I hope that employees continue to agitate against them! But as a former employee of Google, I am under no illusions that AWU would have represented my interests as an employee. Primarily, they are a political action committee set up by an extremely vocal minority of Google's employees to further those employees' political goals.