Edgybees Senior Computer Vision Engineer interview questions

I'd undergone 6 interviews (4 technical interviews and 2 additional interviews with upper management) and was asked to complete 2 home assignments. I was led to believe I was successful at each stage. The last 2 interviews were at their headquarters with upper management, implying that the process was continuing in a positive direction. Upon notification of their decision not to hire me, they expressed that I don't possess the technical skills required for their position based solely on the third interview. I was surprised by their decision. I don't understand why they needed me to invest my time and efforts in vein when the decision had already been made by the third interview. Companies need to find a way to both evaluate interviewees while acknowledging their endeavors. In this situation that was not the case in my experience.