Aigen interview questions

30 min call with recruiter. 45 min call with CTO. 3.5 hours onsite with 3 engineers and CEO + CTO. It was a fairly quick and straight forward process that lasted for a couple weeks. I felt positive after the interview but got sent a fairly generic rejection email about a week later. It was frustrating that despite dedicating 6-7 hours of my personal time, the team did not provide any feedback as to where and how I could improve. That's the least I would expect.