Really? You have never seen anyone look at a sales forecast? You have led a very sheltered life then. Or do you imagine that sales forecasts are not an assessment of expected demand?
Yes, people look at how much they expect their product to sell and what price they can sell it at. They do not confuse this with "aggregate demand".
They do not sit around modeling things like "lets do an upside case where the government takes more of our profit and uses it to make aggregate demand higher."
I see why you are normally reluctant to do more than just asking pointless questions, you really don't understand this very well. No one, except you, is confusing price setting with aggregate demand.
Demand is more than the desire to buy things, people have to have the money required to buy things. If they don't have the money required to buy products and services one of two things happen, and neither is good. They don't buy anything or they go into debt to buy more than they can afford. This is just common sense.
The government doesn't take money from the corporations to make demand higher, but the government does largely determine the split between profits and wages. The modern industrial economy produces a tremendous surplus above the amount needed for survival. It is the government's job to decide how much of the annual growth in the surplus goes to profits and how much goes to wages. Without the intercession of the government eventually all of the growth in the economy from improved productivity and innovation will go to profits and wages will slowly decline relative to inflation. This is undesirable, we need a balance between supply and demand, between profits and wages.
The current government, movement conservatism, neoliberal philosophy is that the government has to subsidize and to maximize profits.
The government's job should be to make sure that the workers have a more equal footing to negotiate wages, to maintain a balance between profits and wages.
The corporation is a wholly artificial creation of the government. It is a creation that we have benefited a great deal from. They allow economies of scale, self-financing, sufficient research and development and a large degree of market control to allow large corporations a comfortable competitive arena conducive to risk taking.
The government provides support to corporations and business in general. It builds the roads, the canals and harbors, the common infrastructure that commerce requires. The government goes on to educate their workers, to protect industry from foreign competition when the industry is young and subsidize their foreign sales. In the past, the government has protected businesses and the economy in general from the worse of the predatory and unstable financial sector, which left on its own engages in alternating between bleeding businesses and consumers dry in a death of a thousand cuts, and collapsing the economy with one of their Ponzi schemes, such as the weaponized mortgage securization that nearly destroyed the world's economy in 2008.
If the government doesn't provide the balance that the economy needs, if it only subsidizes the corporations, you end up with what we have had for the last four decades, a low growth economy with low inflation, The Great Moderation, and ever increasing income inequality, and the resultant social stress from it that can be expressed in many ways, including electing a proto-fascist, incompetent buffoon as president. Most importantly this is an increasingly unstable condition in the economy. It can't last and the longer it continues the more chaotic the crash will be when it comes.