You know they actually don't, right?
Just because /some/ of those blue bits have the highest /concentrations/ of people in the US, that in no way equates to them having the majority of people.
Sure, most of the red parts don't have a lot of people /per acre/, relatively speaking, but there is a HELL of a lot more acreage to cover, and much of it is acreage that's actually important to the well-being of the country. (IE if/when society collapses, the bread basket will be far more useful than silicon valley.)
But just so you don't think I'm blowing smoke out of my ass, I did a little rough calculation.
Total population of the US: approximately 329 million.
Total population of all red states, plus half of Maine, combined: approximately 188 million.
Therefore, total population of blue states: 329 - 188 = 141 million (approximately)
Now, of course you can say "not all people in the red areas actually voted red!", but the converse is also true; not everyone in California or New York (among the few other tiny blue areas) voted blue. In fact I'm given to understand there's a fairly large "red" contingent in California.
It's the sheer, utterly disgusting arrogance of the you people that lets you think that living in elite, wealthy, decadent cities makes your opinions more important than the hard-working people on their "dusty land" in your so-called "flyover states", and that just because they're spread out in many states instead of all clustered in one or two cities, that means you are "obviously" the majority.
It's your kind of thinking that will lead to the kind of society depicted in the 'Hunger Games' movies. But maybe that's what you want?
And I'm sure you're wondering from where I got my population figures.
For population of individual states: http://worldpopulationreview.com/states/
For political position of each state as of 2016 election: https://en.wikipedia.org/wiki/Red_states_and_blue_states#Table_of_presidential_elections_by_states_since_1972