To provide better control over security.
IPSec protocol can be used to estabilish Virtual Private Networks, thus give secure access to everyone who has access (on organization level).
SSL VPN's allow more precise access control (and access to resources according to role / security level). They provide connections between endpoints, rather than securing communication across the entire organization.
Application layer security measures can take form of authentication / authorization (so different users can access network from the same device, to identify them and give appropriate service).