There have been hundreds of unsuccessful proposed amendments to modify or abolish the Electoral College - more than any other subject of Constitutional reform.
To abolish the Electoral College would need a constitutional amendment, and could be stopped by states with as little as 3% of the U.S. population.

Instead, by changing state laws, without changing anything in the Constitution, using the built-in method that the Constitution provides for states to make changes, the National Popular Vote bill is 61% of the way to guaranteeing the presidency to the candidate who receives the most popular votes in the country. 

Every vote, everywhere, would be politically relevant and equal in every presidential election.  
There would no longer be a handful of 'battleground' states where voters and policies are more important than those of the voters in 38+ predictable states that have just been 'spectators' and ignored after the conventions.