Edit: Oh, I see where you're coming from in light of the parent. Well, Google could place ads inside their product without actually running an ad network—that is in fact what most websites on the internet do.
This wouldn't necessarily make sense at Google's scale though, so I don't think that's what GP meant. Rather, Google shouldn't be able to own most of the ad networks on the web while also running massive ad-supported properties in house.
Ad networks were separate years ago! Strangely enough they were acquired. Google bought AdSense and Sprinks in 2003, dMark Broadcasting in 2006, AdScape and DoubleClick in 2007, AdMob in 2009, Invite Media in 2010, mDialog in 2014, Red Hot Labs in 2015... I'm sure there are more.
Edit: Oh, I see where you're coming from in light of the parent. Well, Google could place ads inside their product without actually running an ad network—that is in fact what most websites on the internet do.
This wouldn't necessarily make sense at Google's scale though, so I don't think that's what GP meant. Rather, Google shouldn't be able to own most of the ad networks on the web while also running massive ad-supported properties in house.