It will decrease development costs for the end users, but most times when you say you want a simple api, you mean you want to take a really complicated system a

It will decrease development costs for the end users, but most times when you say you want a simple api, you mean you want to take a really complicated system and wrap it up in a far simpler interface (hence the "abstract" part). Making good abstractions for a complicated system is always harder than just a 1:1 API.