1. Concerns about censorship of research critical of Google.
2. Concerns about diversity efforts within the Research organization.
Replacing someone with a proven track record of being above-average on diversity work, even to his own detriment, and who was willing to fight for his reports when they were censored by higher ups (Samy) with someone who is at best an unknown quantity (Marian) does not instill confidence.
Further, the claimed changes don't really do much. Supposedly, failures of DEI will be more impactful on perf for executives. Does that mean that the executives involved in this sequence of events will be dinged for mishandling this? My impression is no, or if anyone is, it'll be Samy.
As a sidebar, there's also the more nefarious thought that if you're being judged on the diversity of your org, firing a black woman and then bringing in a black woman executive means you won't get dinged for DE&I failures. Hence: tokenism without addressing the underlying issues, which might be summed up as many of the employees have no confidence in management.