There were errors on your cover letter/resume or the documents weren’t tailored for the job that you applied for.
Another candidate met the desired qualifications and requirements more closely than you.
You weren’t prepared for the interview. Do you know your short-term and long-term career goals? Why did you apply for this job?
Social media habits raised red flags. Hiring managers who search applicants online will not be impressed when they see inappropriate pictures or content and/or negative feedback towards jobs or previous employers.
Your comments and questions weren’t job-related; instead, they were focused on the company’s perks like salary, benefits, etc.
You didn’t follow up. One in four hiring managers believes candidates who don’t send a thank you or follow up won’t be a good fit for the job.