When an appraiser inspects, they are doing more than rote measurements and photos - the appraiser is gathering personal observations and may also talk to owners and real estate agents on site, gathering impressions of the neighborhood and site, and if they drive the comps as part of the assignment, form an opinion about them as well.
Working from the notes and photos oa a third party is like reading teh list f ingredients and seeing a food photo vs the experience of tasting and eating the actual meal.
A nurse is under the supervision of the MD and a nurse needs their own license and months/years of training -just to take a BP or temp.