I think what you have there is a monolithic HR application and a smaller monolithic pet insurance application that exchange information via enterprise integration, not a microservice architecture.
But as a customer, if I have a HR app from vendor A, and then I want to add a pet insurance app from vendor B, the last thing I want to do is to roll out some creaky enterprise integration process/framework/product. If those products work together via APIs why should I take any of the burden of integration?
"APIs" are an enterprise integration technique [1]. There's nothing inherently creaky or frameworkey about them.
[1] http://www.enterpriseintegrationpatterns.com/patterns/messag...