That is the culture part.
Being an active conservative in may fields is a job ending event. In certain fields, massive pressure is put on you to conform to the liberal line (my bride is a teacher).
Most people will not stand up to the pressure.
And it isn’t just the raw numbers, but where those numbers are. California, Texas, and many other states have high concentrations of Latino’s and minorities. They will swing the election by their electoral votes alone.
In the 2014 midterms, the Dems could only get 33% of the white vote in NC and other states in the South.