Power is transmitted at very high voltage to reduce transmission looses.,When we raise voltage for transmission we get less current for same power. power loss is depend upon current .
For the purpose of Safety we can not use very high voltage like 800KV or 400KV..Here voltage is reduced by transformers to 440/220/110 etc. Domestic equipment s runs on low voltage for safety. Higher voltage means very thick insulation which could not be made in small equipment...