Why do students have such a hard time going from word statement to solution formulation? Modelling is pattern recognition which is inherent in our way of thinking, so we are all capable, to some degree at least, of being able to abstract a mental model. Our lives are full of concepts (mother, hot, cold, up, left, etc). It is a stylization of reality. A triangle is a model. They are all constructs of the mind to facilitate manipulation. An idea is a model. We lump concepts to build up a hierarchy of concepts to form more complex, layered models.
What are the barriers to modelling? Perhaps it is a lack of confidence or the simple inability to see a path forward. There is a natural reluctance to not start until you can see the whole solution. To counter this, as educators, perhaps we can set it up so that the problem is more open ended. Ask how the problem can be simulated. Break it down into parts. Ask how each individual effect can be modelled. Later, once these small steps are mastered, ask how to bring it together as a system. Maybe that is the issue. Modelling is a systems activity whereas the students are still on the components level. Modelling is higher up on Bloom's hierarchy.