Reaching the age of adolescence can be really stressful, since there are gym classes and hot days when you sweat a lot and smell bad. To avoid the smelly part, more than 90% of teenagers and adults in US use antiperspirant or deodorant to neutralize the odor. This became a universal rule and even 78% of the people should never use deodorant because of the genes but they still do.
You need to understand that sweat does not smell. The general thought is that we smell because we sweat a lot. However, this is now true since the bacteria in the armpit releases that awful smell. The lipids and amino acids in the sweat can be easily break down by the bacteria and they will transform into substances with different smell which is our body odor.