Intuit interview questions

It started last month in January where they had given open ended question to create API for one of their project. I implemented it pretty good and added more things than were asked. So I was called for onsite interview. They asked me to improve on the same project I worked on before. I did well and implemented whatever they asked except one question in two - three rounds of interview. Now they rejected me by saying I haven't covered small things in my project in first round. I don't understand why they called me onsite if they didn't like the project at first place. You cannot expect to develop production ready stuff in 4-6 hours. especially when you say its open ended question. Worst interview process.