SendGrid Software Developer interview questions

Initial 30 minute phone screen consisting of behavioral questions, technical questions, and inquiries about previous projects. I passed this phone screen and advanced to the next stage which was a take-home technical challenge. This challenge involved building a simple single page web app in HTML, CSS, and jQuery after fetching data and images from a provided API. I spent about 8 hours on this technical challenge and showed it to some colleagues to look over before submitting. As far as we all could tell, it worked perfectly, satisfied all the requirements, and contained several features to make it look more like the provided comp (even though these features were not listed as requirements). The SendGrid recruiter I was working with informed me about a week later that they would not be proceeding with my application, but was friendly and offered to answer any questions I might have. I wrote back asking for some feedback about my submitted tech challenge to learn if I had inadvertently made some mistakes. No response, as is unfortunately typical for many companies. Whether it was due to the companies lack or organization or consideration for candidates who invest time in these challenge, I don't know.