Circus Kitchens interview questions

I had 5 interviews total, had to do a case study that took around 6 hours. Interviews in order where: HR interview, line manager, line manager + another manager to go through case study, in office interview, CTO interview. It was way too many interviews with way too much effort required on my part. I asked for at least some feedback on why they rejected me after this many rounds and they just ghosted me (after also ignoring a deadline we agreed on for feedback regarding the whole application.). A rejection is completely fine, but I feel that they were not fair regarding the whole process and communication (or lack of it) after having required this much effort on the applicant's side. The case study seemed to feature an issue they were or are still struggling with. After talking to them, I feel like they might be collecting ideas from people using the premise of a case study.