Because the computer can't react in the same way a casino will. It is dynamic. It is not predictable and is dependent on human variables not a science. That can't be simmed. It is like simming what route I might take while hunting in the woods. I might like to keep the wind in my face and the sun at my back while sticking to the shadows and quieter ground to move across using terrain to my advantage considering how it will affect wind patterns by creating eddies and blind spots for areas that are ahead but I will encounter sign and interact with living beings and react to their reaction and alter my computer optimal path as I encounter these. There is no way to put actual odds to such a fluid dynamic. You can try but it would be a lie to expect any sort of accuracy. You would just be fooling yourself.

Analyzing your play in retrospect and averaging the data from the sims to how you react at a given casino with the team you encounter in the pit is the only way to get a realistic view of the return given how you must play at a given casino and shift. Such fluid systems that react to unpredictable stimuli make for poor results when you start predicting the stimuli. Like they say garbage in garbage out. The sim will tell you your results for a predictable reaction to your presence and what you might do when you encounter same. If only it were that easy everyone could play longer sessions for a big spread and top bet without getting backed off. In reality only the true artists of our profession can pull that off. We all can master the math and most can use it in a casino but there is so much more to what we do than that.