Hopper Staff Software Engineer interview questions

Recruiter reached out to me about open position. They kept me hanging for few weeks while also slowly progressing with the interview. Halfway through though, they had already selected the candidate and stopped the process. Why interview multiple candidates when you already have candidates in line? I would suggest using this company as a test ground and probably not offer them as much value as you know they're using you as a test candidate. (Also current employees told me there is no real job security as when recession comes, this company if one of the first to let employees go)