Is it okay to ask a firm why they didn’t give me a full-time offer?

I did a busy season internship for a mid sized firm in Chicago this year and I was expecting a full-time offer but didn’t get one. I was caught off guard because one of the partners I worked for told me he wanted me to come back to the firm and I told him I was definitely interested in doing that. But, like I said, I didn’t get an offer. I assumed it was because I was too far away from completing 150 hours (a year from the internship) so after waiting a semester, I applied there for a full-time spot and didn’t even get an interview. Would it be a bad idea to email the partner and ask him why they decided they didn’t want me to work there? It’s been a while since the internship (6 months) and I wouldn’t want to come off as rude or something.