AD Audit plus license question

AD Audit plus license question

Hello
I have a license related question that I am trying to figure and any input will be appreciated.
lets assume a company has roughly around 6000 workstations, 500 servers, and 5 domain controllers.
And they have the following licenses/Subscriptions:
1. ManageEngine AD360 ADAudit Plus Professional Edition - Subscription Model -Annual Subscription fee for 5 Domain Controllers
2. ManageEngine AD360 ADAudit Plus Professional Edition - Subscription Model -Annual Subscription fee for 500 member servers
3. ManageEngine AD360 ADAudit Plus Professional Edition - Subscription Model -Annual Subscription fee for 6000 workstations.

AD Audit plus pulls logs from all Domain controllers right, my question is:
Why would they need ADAudit plus subscription for all 6000 workstations and 500 member servers when it can pull all the AD related logs from Domain Controllers which it already has license?
Any justification for having the same license for all of them?

Isn't it better to have an EventLog Analyzer license/subscription for all the workstations & servers rather than ADAudit Plus license?

Thanks in advance!