Why did Al gore lose the 2000 election?

He lost the electoral vote. He got more popular votes but those don't matter.

Had Al Gore won one more state (even a 3-electoral vote state like Wyoming) he would have been the president from 2001-2005. Also Joe Lieberman would have become the first Jewish vice president.
Because he did not win 270 electoral votes. Yes, he did win the popular vote, but he had won by more states in the states he won, and a closer margin in the states that he lost.