Google Software Engineer - Internship interview questions

First, I gave online assessment which had two easy-medium questions. Few weeks later I got an email to schedule two phone interviews. Interviews went well and the next day the recruiter asked me to setup one additional phone interview as they need some more data points. Two weeks later I had my third interview. It also went well. Overall, none of three interviews went bad, I'm pretty sure that I aced two of them. Few days later I got an email from the recruiter saying I'm rejected. No reason mentioned. I feel the bar is very high for the grad students.