Stock Photography is a field of scope more broad than portraiture because it does not cause an emotional attachment alone.
Stock (at-least in my opinion) includes styles Commercial, Product, Scenic, Wildlife, Botany, Oceanic, Astronomic, Architectural and Historical opportunities giving objects to be the primary focus in the photo.
Portraiture ought to emphasize the person over their surroundings, even if the photograph is not designed to prominently showcase the subject.
The difference between Stock and Portraiture is in the photograph’s use. For instance, a company selling a consumable product will use a photograph of the product for visual communication is a use of stock but meant to sell a different product than the photograph.
The Stock Photography industry is designed to sell photographs, rather than photographs being used to sell other products.
It is important to consider the purpose of the photograph whether displaying it in home or sale. Just as a photographer is critiqued for how they captured the subject and displayed the photo’s purpose, so an image out-of-place or incompatible with its surroundings is important to consider when placed.
If a portrait is placed in a photo frame intended to be used as a stock photograph but is an obvious portrait of the subject, it looks out-of-place as it sits on the store shelf. There are aesthetic changes that can be made to the portrait to show the commercial use, but without these changes it would seem that someone had left a framed photo at the store as they shopped for a new picture frame.
The same principle applies to stock photography. If a person or an object is in the photograph distracting from the photographic statement, it is better to change perspectives or wait until the person leaves the frame and not “shoot around them”.
One of the best investments in a shot is time. Do not be afraid to invest!