What is stopping humanity from developing a way of keeping the brain alive indefinitely?

Our brain is kept alive in our bodies because of many different variables.

Why can't we replicate these variables in order to preserve the brain, and as a result, the conscious and sub-concious of a individual human.

As a result of what I am suggesting, our ability to think will be retained, however, due to the lack of a body, the brain will be devoid of all external stimuli.

Also, on a separate note, is it possible to let the brain experience stimuli artificially? Stimulating certain points of the brain in order to inject stimuli such as a certain smell, a vision, a touch, etc.