Their point is that people do pay for these services and they have still introduced ads to squeeze out more revenue. Ergo, paying for a service guarantees nothing.
The one and only exception was the movie "Person of Interest" which was FreeVee only for reasons I do not understand so I put up with their ads and then purchased the box set on DVD. The ads were so weird it was entertaining to watch them. They were clearly all created in China and I am still not convinced the actors were real people.
Becoming a paying customer is just a negotiation with advertisers to raise their rates until Netflix concedes to what they want. Since they know you have more discretionary income Netflix can also charge more for ads. They're also incentivized into turning those customers into ad supported by increasing the no ad plan cost.