First off, not everyone who doesn’t wear deodorant smells, and secondly, some people shower regularly and use deodorant and still smell.
The diet, genetics, and what kind of bacteria live on your skin will affect the body’s odor. I struggled with body odor for years before I discovered that I was showering incorrectly. I learned that after lathering the soap and getting covered by it, you’re supposed to let it sit on the skin for a while before scrubbing and rinsing; this discovery which many consider obvious was new to me, and it stopped my body odour completely to the point I don’t need deodorant at all by simply showering with a correct technique.