C-4 Analytics interview questions

I went through 5 rounds of interviews with C-4, all with people at various levels of the organization. I blew through rounds 1-4 with flying colors and had great feedback every step of the way. For the final round, round 5, they asked me to conduct and present a digital audit of a company of my choosing. I very thoroughly conducted this audit, put it into a slide show presentation, and practiced for multiple days in preparation. In total, I invested about 10 hours of work into pulling the data, conducting a baseline analysis, writing my insights and recommendations, practicing, etc.. (Mind you, I do this all of the time in my current role so I know I did well). I presented it to 3 members of their team and felt like I handled all of the questions in the Q+A portion really well, only to be rejected 6 days later. In total, I invested over 12 hours (yes, 12) into this interview process and was genuinely expecting an offer at the end of this. They told me they went with a candidate who they felt had experience that was "more in line with what they were looking for." I replied to my rejection email expressing my surprise and and asked for specific feedback that I could use to better myself for future interviews, only to be completely ghosted. I was obviously very let down by this whole thing. If they felt my experience was not what they needed, I don't know why they continued to waste my time. Could they not figure that out by round 2 or 3? Or surely before I invested over 10 hours in conducting and presenting an entire audit? I will say that their HR team is professional and really on top of it, and they usually got back to me quickly. They clearly have a very fine-tuned hiring process (probably due to their high turnover rate from what I've seen on their Glassdoor account). Overall the process was fine, but I do feel like they wasted my time and gave me a pretty crappy excuse as to why I didn't receive and offer. Also really dislike that they didn't even respond to my last email asking where I could improve.

Process was 6 rounds long. Pretty repetitive interviews, was asked almost the same exact questions in every one. Had to call after the 6th interview because no one had gotten back to me in a few weeks.