Only because the state monopolises such projects through taxation, regulation, licensing laws etc.
There are already examples of private investment achieving in these areas despite all of the above. I think private enterprise will eventually take over, but it will be a long battle.
Would private enterprise really fund fundamental research, such as particle physics at CERN or astronomy? These things are important for our understanding of the nature and the universe, but the economic return is extremely hard to predict, although sometimes very large. Who would have thought that something like the world wide web would originate from particle physics? The returns from fundamental research can be several decades later.
There are already examples of private investment achieving in these areas despite all of the above. I think private enterprise will eventually take over, but it will be a long battle.