The reason is simple. A bad fit usually causes discomfort and pain, and you end up not wearing the shoes. Many people have gone through the experience of either hiring someone who doesn't fit the job, or of working in a job in which they themselves don't fit. The results are disruptive at best and disastrous at worst.
Most employers rely almost exclusively on the employment interview to assess candidates.
They may even check references. Unfortunately, the employment interview is one of the least accurate predictors of success on the job. In the job interview, candidates present their best sides in order to obtain the job. Add to that the explosion in the number of classes and groups which coach candidates on filling out applications, writing resum s and conducting themselves during an interview. Reference checks are excellent selection tools - if you can get a former employer to give you a candid one.