Wild Swing in Participation

As everyone knows by now, Donald Trump has won the election and thus will be the second president to serve non-consecutive terms.  Grover Cleveland served as both the 22nd and 24th President.  That's interesting, but what I find more interesting is the vote totals in the last several elections:

These are the vote totals for Democrat and Republican candidates over the last 5 elections.  As this doesn't consider 3rd parties, it is just ballpark but useful.  Here it is as a chart:

2008 was a banner year, the biggest turnout ever in which President Obama won nearly 70 million votes but his reelection in 2012 saw a drop off in participation of roughly 2.5 million voters.

2016 exceeded 2008 in total voters (Trump and Hillary drove a surprising number of voters to the 3rd parties) but the two parties only received about 2 million more votes than in 2012.

2020 blew the doors off all previous elections, seeing nearly 27 million more voters than 2016!

As of this writing, 2024 has seen a stunning drop of 16 million voters.  Where did they go?  Is this a matter of apathy, tougher voting requirements, or something else?  A ballot arriving in the mailbox while everyone was quarantined by COVID offered a distraction whereas today voting was just a hassle?  This will be a topic for the history books in the not-too-distant future.