I see where you are coming from, but it's not being called an ad company because it relies on ads to operate. It's being called an ad company because that's the product it primarily sells. It's the same reason we don't call Ford a robotics company and we don't call McDonald's a supply chain company.

I'm fine with calling it a tech company as well because they create a lot of tech at the same time, but your comparisons to other dependencies are false equivalences. Google depends on selling ads, not using ads. Google doesn't depend on selling engineers, they use engineers. Google doesn't depend on selling the web, they use the web. Get it?