Most companies are bought up and owned but larger corporations, these guys own so many products and are large shareholders in almost everything, other then super small local ads the rest is owned by some company that is owned by some other company that is owned by some massive corporation.
There are cases where a subsidiary company advertises on a related subsidiary’s network (for example, a Dreamworks movie being advertised during a Flyers game which is broadcast on Peacock, all three entities ultimately owned by Comcast) but:
a) That doesn’t mean Comcast is actively running all three of those companies. They each independently have their own revenue and expenses, their own leadership, decision making, etc. Comcast is just a group of investors with a leash on the CEO and an organizing force to make sure the subsidiaries are partnered to create efficiencies.
b) The great majority of ads
don’t come from Comcast entities. For example Comcast doesn’t make beer, or restaurants, or cars.