The OP is assuming that funds being directed towards a campus is extraneous spending that could've been directed towards making products better instead.
If they knew anything about Google they’d understand how wrong that is.
If any human organization to ever exist on the face of the earth has enough money, it is Google.
The reason why their products increasingly can seem long in the tooth is that corporate work is a huge game of telephone, where messages from the top to the bottom and vice versa get horribly garbled.
Add in a culture that rewards shipping features, but not necessarily good ones.
This is hard to believe given the quality of most software, but at some point, one might expect a decline in product quality to harm revenue and profitability, which would reduce or eliminate the need for headcount growth.