I think the problem is that most Americans do not understand or care about politics.
a look at https://en.wikipedia.org/wiki/Voter_turnout_in_the_United_States_presidential_elections supports your supposition.
I looked at that right after Nov 2016. I came up with the theory that Republicans have reached their maximum votes, around about 60 million and will only grow as a percentage of the total population. Whereas Democrats can draw on a much larger pool of disaffected and apathetic voters by coming up with candidates who have something exciting to offer. Obama received 68 million votes for example.
A key factor is the youth vote has been down since Nixon. Politics has been about the “establishment” since then. It’s a meaningless term since it has been applied to Nixon and Clinton. I looked at that again recently and this year will be interesting. It appears youth are finding a voice. They are dealing with social media. It’s now the old man in the White House who tweets idiotic garbage. Their protests are non-violent, and not weird, like Occupy. They don’t mistrust people over 30, they choose mentors. Their demographic is going to dominate for a few decades. Hopefully they will vote more consistently than my Gen X/Baby Boomers did.