I would have to guess as we lack any comparisons, but most probably lighting and composition as well as setting and context are the most likely issues.
Pose alone does not make a good shot. If the pose is in a context that is unexpected for the viewer it can be disconcerting.
Lighting is very important. If there is one thing that differentiates great photographers from mediocre ones ( like me ) it's the use of light. They tend to have a much better understanding of how to light, what to light and how to use both available and artificial light. It's a talent, as well as a learned skill. I tend to think of this as the defining difference.
Composition. Well many people have good composition, but again, can't quite make it from good to great. It's talent rather than learned, IMO, although learning helps.
But top of the list of suspects : use of light.