Why do I have a trial when I can pay for my ticket?

They get to I96 and as I was going around the turn. My tire blew out and I slipped out on some ice. A person asked me if I was okay and I said yes. As I was getting out of the van, a police officer pulled up and asked me if I was okay and I told him yes. He asked me questions and I answered them. Then another car had slipped out towards us and the officer pulled me back as another car slipped. The officer let them go and gave me a breath test. He never gave me a ticket but arrested me for two tickets that I thought that I had paid on. I was in jail for 5 days so when I get out and paid those two tickets off, I found out that I had warrant but I was never issued a ticket. The warrant was just in the computer for six months. I walked in to the court room to see if I can pay the ticket. The court appointed lawyer did all the talking and said I plead not guilty to under influence. She wanted to take it to trial and now I’m out on personal bond until trial. All I wanted was to pay my ticket. I don't know what to do or expect or why did she want to take this to trial. I didn't hit a car or anyone.