It's more likely a cost benefit analysis. Fighting the Unions is lawyer expensive and PR expensive. Gamers are noisy after all, when riled up. Microsoft is evil, but also like Trump, they understand optics.
I think it might be more subtle than that, unions exist so that when negotiations happen they can fuck back, but we know Microsoft can strategise longer term than that. They pioneered "embrace, extend, extinguish". Embracing a union then trying to infiltrate and turn it into a corporatised union is another version of that exact same play.
Companies can leverage CBAs to "fix" pay scales well below CPI or other metrics by forcing extensive negotiation as a way to sell down an agreement. Similarly, they can use agreements to create separate classes, for example: the SAG/AFTRA agreement for voice actors with all the Gen AI exemptions.