The electoral college was designed to give small states a decent say. Now, a handful are decisive. At least 40 states are solid democrat or solid Republican. The electorate is inelastic, both in terms of the state results and the votes within them.Hilary Clinton got over 2.8 million more popular votes but still lost to Donald Trump. Probably a better example of how the above could happen.
In swing states, I guess 45% is immovable for each side with maybe 10% fluid. A few voters hold the presidency in their hands and change is exceedingly slow.