MORSE Corp Software Engineer Co Op interview questions

The process was really quick and efficient. Started with a quick recruiter call explaining how the process would work. Then the next day I had a very simple tech interview with an engineer. The next week I interviewed with someone from HR. This interview wasn't very behavioral, it mainly confirmed my interest in the role and would I be okay working on military software. I feel that both of my interviews went great and that it was a good fit. After the last interview, however, they ghosted me for a week after saying I'd get feedback by the end of the week and they did not give me an offer. I suspect it's because I am a DS major and showed interest in DS/ML projects as well as software development. Not sure why they interviewed me for this role if they didn't want a DS major to begin with. They reached out to all my references, got positive reviews and still didn't give me the offer. That is very unprofessional. Do not reach out to references if you have no intention of offering that person the job.