Existing Controller Schemes
There are MANY different types of communication schemes used for Controls Systems. There are controls that communicate over wires that connect them together. Some send data to each other using radio transceivers (Bluetooth, WIFI, Zigbee, ZWave etc.). Others transmit data over electric wires that power the devices (X10, UPB, etc.).

So why re-invent the wheel? They all work to control lots of different things however they don't really work together. These different communication schemes aren't really compatible. The better question might be, why do the current "wheels" cost so much and why are they so hard to install and use? There are a few reasons that current solutions are expensive. Its partly because the hardware itself is expensive. This can be because of licensing fees or because the hardware is sophisticated and complicated to implement. Another reason is the relatively small scale of the production. Compared to the number of homes and businesses in the world, there are very very few control systems installed. Also, the companies that sell automation products like everybody else, want to make a profit and if they can't maximize profits by selling more product, they will charge more per device making the market stay small.