Some shoot wide open to facilitate the subject of the image being easier, quicker to read within the context of the total image. That is a viewer, particularly one skimming many images, will comprehend the image quickly.
Some shoot wide open or at larger apertures as a by-product of using slow films for a particular look, ie, minimal grain, smooth tone transitions; likewise for low ISO ratings to reduce digital noise.
Some use older lenses, such as my own Canon 50/1.2 LTM, with the understanding that certain aberrations will be more prominent at larger apertures for a particular look, which likewise limits depth of field.
Some portraitists use longer lenses at wider apertures understanding that the limited DoF will smooth over skin imperfections of their subjects.
Some jump on the bandwagon of the latest fad. I recall back in the '70's when many (too many) were shooting 2475 Recording Film and abusing it in processing to accentuate grain, a photo variant of pointilism.
Then there are those who previsualize an image and choose the variables at hand to achieve a specific look, leaving as little to chance as possible. The range of DoF is known as is also what will fall in that zone and what will be excluded. The range of light is known and exposure (and it follows also development) is made to achieve a desired contrast. Lens selection is made on the basis of perspective and the characteristics of a given lens.