A reason for that is that with cloud services it is (in general) challenging to connect to an on-premise Active Directory. If you have applications in your network, they can communicate via LDAP or Kerberos to your Active Directory directly.
As cloud services reside on the internet, there are firewalls that protect access from the internet to your AD servers, and I know few organizations that would allow such direct inbound traffic from the internet.
Enterprise authentication for cloud services will typically run over a kind of Single Sign On solution, which can do the authentication on behalf of the cloud service, and has access to the user authentication databases. Azure AD is one example, where you can synchronize a local Active Directory. Another (on-prem) solution for Active Directory is MS AD Federation Services, which implements SAML (needed for the Central SSO) and more. Also there are cloud identity providers that can do similar things 'as a service'. If you have ClearPass running, you could even use ClearPass as an IdP (identity provider) for Central SSO.
So, in short, you will need to find some SAML SSO Identity Provider that links to your AD to implement this type of cloud authentication with Central.