"What is the main reason so many do not believe in a Creator...and choose evolution?"

OP, I will answer you to the best of my ability.

First, you're asking two different questions. There are many that believe in God and evolution. This website was made by Christians who accept the scientific consensus regarding the age of the Earth, and evolution: [link to biologos.org (secure)]

Now, the main reason people don't believe in a 'Creator' is because they simply weren't raised to do so, and/or they haven't seen sufficient evidence for one.

As for why people choose evolution... choose is a strange word to use. I don't choose to believe in germs, or gravity, I am convinced of them by evidence. People are convinced of evolution because there is a lot of evidence for it. I can't stress that enough, the evidence is overwhelming, and every test that our best minds can come up with points to evolution theory being correct.

Creationists will tell you that it's because we want to live in sin or some such personal slander, but the simple answer is evidence.