The system of making the loser of the presidential election vice president was ended because

The system of making the loser of the presidential election vice president was ended because: the two leaders might be political enemies.

Explanation:

In 1804 the 12th Amendment to the Constitution was ratified so that the position of vice president of the United States stop going to the runner-up in the presidential election and become a separately elected office.

Such an amendment was proposed after the 1796 election which resulted in a president (John Adams) and vice president (Thomas Jefferson) who belonged to opposing parties.