A small hand individuals run the entire United States, they impose all the rules and currently have no limits to the amount of time that can be spent as a politican.
Unfortunately this has caused these 545 individuals to choose politics as a career and impose regulations and rules that pertain to their personal interests. Once laws are passed, they are extremely difficult to abolish. The careers of these politicans have done far greater distruction then good and have resulted in the United States current economic slump due to unnecessary spending on agencies and promises to the people that cannot be supported in the future.
Imposing term limits of 4 years allows for the people to reguarly voice their opinions on issues and acts as a check and balance on the system as a whole.