Here are some common reasons:
Security is rarely the "top of mind" priority for an application developer, and therefore it's often bolted on as an afterthought.
Most enterprises have a mix of technologies and using different vendor interfaces adds to programming complexity.
Finally with the ever growing threat landscape, frequent changes in the security layer require changes in applications, requiring security and application teams to collaborate and impacting timelines and delivery.
iamAPI provides a consistent, secure, REST based API suite for user registration, authentication and authorization.
The API abstracts underlying technologies and allows application developers to leverage centralized IAM frameworks to manage employees, vendors, consumers etc.
Changes in technology or vendor API can be localized within iamAPI, leaving applications that use it unchanged.