I do not know how people can go days without showering. Unless you are a newborn baby or in a survival situation with no running water, there is no excuse for not hopping in the shower for 10 minutes a day and lathering up your whole body. You do not need 10 million different gels and conditioners to be clean, contrary to what some clean consumers believe. As long as you shower, wash your sheets, and wear deodorant, you really can't go wrong. It's not rocket science.
There are some unsubstantiated rumors going around that you don't need to shower every day if you are generally clean in every other area of your life, and that's just not true. You definitely do not need to wash your hair with shampoo and conditioner every day to be clean, but if the largest organ on your body goes mostly unwashed for days at a time, you shouldn't be surprised that you stink. Just because you don't smell it doesn't mean that everyone else can't, and you should be considerate of other people's nostrils.
Should smelling badly prevent you from having a job? It is definitely unprofessional behavior, whether you like that classification of "smelliness" or not. But sometimes, it's just as unprofessional to tell someone that they smell as it is to be the smelly person. A professional took to r/Advice to ask what to do about her coworker, who keeps making passive-aggressive comments about her scent. The employee is hygienic, showering regularly, and even went to the doctor to see if this percieved scent could be from some medical issue.