Why did voters elect Biden in 2020 over Trump, only to elect Trump 4 years later, where's the sense in that?

Swing voting, is all I can think of, or voters who are bipolar/moody? Like the weather? Whichever way the wind blows πŸŒ¬οΈπŸƒ shrugs - surely I'm asking a fair question here as an Aussie, American voters kicked out The Donald in 2020, after only one 4 year term, and then, 4 years later, have elected him back in again for one last 2nd term. Why and I'm asking "the why" as in a deeper, how come? πŸ«΄πŸ»πŸ’­
Swing voters
The mentally ill
Hard to determine
Other
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Why did voters elect Biden in 2020 over Trump, only to elect Trump 4 years later, where's the sense in that?
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