Pacmann AI interview questions

They posted a vacancy and those shortlisted candidates were asked to do an assignment in which we had to analyze and propose solutions to address the shortcomings of their online classes. There were 100+ data and I wasted many hours to finish it. After my submission, I made it to the next interview and a week later they suddenly announced that they wouldn't hire anyone for this role due to internal changes. That's so unprofessional and unethical if Pacmann only wanted to extract others' ideas and works without hiring them. Kudos to the C level though for not thinking this through completely before they posted a vacancy. I guess that "internal changes" referred to the tech winter? or maybe it's a strategy to get things done for free in the name of hiring process? I never know.