LinkedIn Software Developer interview questions

Got contacted by a recruiter via linkedin. Did an initial phone interview on ml concepts and coding and according to the recruiter it went so well that they did not need me to do another one. Got invited to the campus for an onsite which I can name more a torture than an interview; staring from about 9:30 am lasting until 5pm. 7 interviews in a day!!!!! Unstructured interview; I was doing the interview for a data science/software engineering position; open ended questions; some interviewers were more after math/theory and some high level software design and some not sure! It was hard to figure who is looking for what and how to form a proper answer. One of the interviewers was a little rude even though he was 15-20 mins late for the interview. Generally not a good experience. The campus and food were great though. Got a call from recruiter a few days later. "Your interview went well but we couldn't find any position for you. I tried to find a team by passing your resume over but unfortunately we don't have an open position at the time"! A simple question for them: Why the hell do you interview people then? Why the hell do you waste people's times by sending bunch of bol... job opening messages over and over? Interesting that after I did the onsite and was waiting for the feedback, there was another linkedIn recruiter contacting me about open engineering position at linkedin!!!!