I think it's plausible that the superfluous hirings are caused by hirings of key individuals. It's quite common for these big tech companies to poach each other

I think it's plausible that the superfluous hirings are caused by hirings of key individuals. It's quite common for these big tech companies to poach each others department heads and other key personnel. This can cause significant damage to a company so can be an attractive tactic. The downside is that in order to retain these people you don't just have to pay them a lot of money you also have to give them big projects and resources to implement them, i.e. lot's of people get hired. This can a problem when these projects aren't supported by the wider company but are just someones pet project.