Why do my feet smell so bad?

Bromohidrosis: This could be either from a bacterial or fungus overgrowth such as in athlete's foot infection. If it is one of the other, especially tinea pedis, then this needs to be treated with anti-fungal agents. If it is evaluated for bromohidrosis, then a anti perspirant can be recommended. You need to have this evaluated.

Smell bad: As already stated your feet may excessively perspire which can lead to other problems. There could be overgrowth of bacteria , fungal infection etc. See your podiatrist for an evaluation as that will get you the answers you seek