I will quote George Washington to explain the why: "However [political parties] may now and then answer popular ends, they are likely in the course of time and things, to become potent engines, by which cunning, ambitious, and unprincipled men will be enabled to subvert the power of the people and to usurp for themselves the reins of government, destroying afterwards the very engines which have lifted them to unjust dominion."
Alternatives:
https://en.wikipedia.org/wiki/Direct_democracy
https://en.wikipedia.org/wiki/Sortition (we use this in 1/3 of our government today - juries)
Advertising, political parties and religions. All of them.