When you run load() in Command Window or through a script, the data is loaded into the 'base' workspace. When you run load() inside a function, the data is loaded into the workspace of that function.
If you Simulink model requires just loading those data but not much processing, you can set up the 'PreLoadFcn' callback of the Simulink model to load the data. If the data needs to be processed before being used by the model, I suggest you do those processing in a script, not in a function.
There are ways to assign data into the 'base' workspace inside a function, such as evalin() or assignin(), but it is not recommended.
If for whatever reason, you have to run that main function, I suggest you adding return arguments to the main function so you can pass data to the 'base' workspace. But of course, if there are many variables, the approach is not very practical.
