In the past people used to sit their televisions on a TV stand or cabinet. Some of these cabinets were beautiful furniture pieces and the doors could be shut to conceal the TV behind. This was ok when the largest screen size TV you could get was 21 inches, but today with flat screen TV sizes regularly in excess of 42 inches, you would need a very large cabinet to house a TV of this size.
Cathode Ray Tube (CRT) TVs were around for a great many years and featured in every living room, but the technology used meant that they were very heavy and bulky. This meant that they could not be moved to a different position easily.
With the introduction of new screen technology, such as plasma and LCD, television sets are now very sleek and slim. This means drastic weight reductions and hence the opportunity arose to mount them on the wall. With the large screen sizes meaning the TV could look like a picture or painting, TV brackets became the best way to mount your TV.