Numerous amount of domain names in various domain extensions are registered every day. However, not all of them are launched as businesses or websites. Most of them serve ads either by registrars (where the domain is registered) or are parked at domain parking services. In either case, it is serving ads and earning revenue sometimes as little as to match the registration and in other cases a lot based on traffic. This .org TLD is a great name for serving Domain Ads related niche.
Great news! Domain DomainAds.org has been registered in the past and previous domain owner(s) may have forgot to renew or dropped it.