Publicly available chat apps are infested with several security issues which can prove detrimental to enterprise-level usage.
Some such issues include:
Inadequate end-to-end encryption
Storage of past conversions
Limited user identity verification abilities
Code unavailable for open review
Inadequate server level that lets the app provider read the messages
Increased possibilities of message interception
Access to other sensitive information/rights in the user device
An enterprise chat app differentiates itself on the above grounds by providing end-to-end encryption, well-designed and documented crypto design, HMAC like encryption, etc.
In short, it is military-grade security for conversations that enterprise-level users will exchange.