The license is the only bit of evidence a homeowner can obtain that gives any indication that the professional is qualified. (Apart from references, but customers almost never actually called the references I would give them.) The license is not a guarantee, nor does it indicate that an unlicensed handyman can’t do a competent job - it’s just all there is. There is always the DIY option, but DIY-inclined homeowners very frequently overestimate their own competence.