Agreed that the OpenAI API is pretty easy to use. But to have a model perform a specific task involves more than just calling the API - you have to manage prompts, finite context windows, and integrations with other APIs.
We use GPT under the hood for our website summarizer for example, which involved connecting the OpenAI API to a web scraper and then handling cases where the website had more text than GPT can handle. Finally we also experimented with a bunch of prompts to make sure that it responds based on the user's needs.