It's doesn't sound like a successful business venture if you're having to increase operation expenses at this rate and not be raking in the revenue.
Yes, Google is profitable now. Tremendously so. But they're at risk of losing revenue and ceasing to be profitable as people cease using Google search and switch to asking questions of their AIs. So to retain their position as the place people go first for information, they have to stay ahead of the AI race. Well, they could also just sit back and wait to see if their competitors are overwhelmed by the query volume, but that risks losing traffic and then having to win it back. It's much better to keep it. And Google is better-positioned to win this race than its competitors both because of its existing infrastructure and expertise and because it already has the eyeballs.
In addition, you seem to be assuming that doubling serving capacity means doubling cost. Clearly Google is not planning to increase their annual operating expenses by 1000X. As the summary actually says in the third paragraph, Google is also going to have to improve efficiency to achieve the growth rate, with better models and better hardware. This is what the AI chief is challenging the employees to do; he's not challenging them to write bigger OPEX checks, that's his job.