You're asking me why independents vote the way they do? Numerous varying reasons is the best I can come up with. Bill Clinton, the man acted presidential. He connected with the people as much as Reagan and FDR did. You never heard Bill call others names or throw temper tantrums. He may have lied to congress, but most folks outside of Republicans either forgave him or didn't care. Bill was a likable guy. Yes, we're back to that with independents.
In 1992 Bill won the independent vote 43-28 over Bush with Perot gaining 30%. A 15 point win among independents. In 1996 Bill won independents 50-30 over Dole with Perot gaining 17%. A 20 Point win among independents. Trump won independents in 2016 by a 46-42 margin with 12% voting third party. A four point margin. Why, likability which you fail to see as a factor. Also Bill was affable, friendly, he wasn't brash or uncouth.
Independents gave Bill a 50% first term approval rating and a great 61% second term approval. So far independents have given Trump a low 39% overall job approval for his first 2 1/2 years. Perhaps independents can be summed up in the numbers of indies who want Trump to run for reelection, 28% do, 49% don't. Question 77.
https://d25d2506sfb94s.cloudfront.net/cumulus_uploads/document/fs1r87zj1f/econTabReport.pdf
Again, these numbers are dynamic and constantly change. I would say Trump today is unpopular with independents. Who knows what these numbers will show come Nov 2020. But they have been fairly constant since Trump first took office. Could be since independents don't pay much attention to politics until a week or two or three prior to the election, they might just want a president who acts presidential and not as a member of the WWE. That's my best guess. But each individual votes the way they do for different reasons.
I said this before, I don't think Republicans, Trump supporters know how much Trump's brash persona, his unique personality hurts him. I'd go so far as to state if Trump had a pleasant, more presidential personality with this good economy, his overall job performance approval would be 10 points higher, perhaps 15.