Wait, the AWU is tiny. I remember the count being something like 2,000 union members out of 100,000 Google employees. It does not make sense for Google to negotiate with it.
The remainder of AWU is people who have put their name on a spreadsheet but have not voted in a union via an NLRB election. The only way to have the legal right to force an employer to bargain with you is to have an NLRB election (or the employer voluntarily recognizes the union).
Google has a legal duty to negotiate in good faith with the 41 Cognizant employees now that the NLRB has found them to be a joint employer. That's true regardless of how small the bargaining unit is. The NLRB found that Google controls essential features of these workers' jobs, which means Google needs to appear at the bargaining table. However, Google is allowed to appeal that finding before it takes effect, which will likely take at least a year in the Federal courts.
You can join a workers union and not have it be recognized by the company. You have fewer legal powers if you go that route, but you can still be a union.
AWU has, iirc, 1500-2000 people. Of those, some small number have voted to force Google to legally recognize the union. The concepts are separate, but related.
I think even if your point is valid, people over at Google are smart and understand that the future is long but precedent is eternal.
And even then, there are in fact these annoying, antiquated laws around labor in the US. They kinda have to at least respond..