Presumably any new product they are building is to increase revenue somewhere, even if it's in another product. They might expect that getting X usage in a chat

Presumably any new product they are building is to increase revenue somewhere, even if it's in another product. They might expect that getting X usage in a chat app will translate to Y additional ads income; due to better tracking data, more chances to show ads, etc. In that case some of the ads revenue could be attributed to the new chat app, based on usage. Some assumptions would need to be made, but the allocations could be tracked, measured, and analyzed pretty well. Of course an approach like this would require some amount of direction and purpose, which is not at all a part of Google's core competencies.