There are hundreds of online articles about why people never vote. This phenomenon is well studied. But they usually study people who never voted in their lives or only vote once in a generation (think Obama 2008).
What isn't discussed often is when someone registers to vote, but doesn't vote. Statistically, once someone is registered to vote they tend to vote. But in most states, 10-33% of registered voters didn't vote in the 2020 presidential election.
I find this odd. Why take the time to register but not vote in the end? There isn't much on the internet to go on.
Two theories
1. People are lazy. Its pretty simple to register online but going out to vote is too much for some folks. Not much different than lazy people who didn't register.
2. Some people don't know they are registered to vote. In my state, the DMV will ask you if you want to register when renewing your licensure. I wouldn't be surprised there are people who say "yes" but don't remember when election time comes
They might not really prefer one candidate over another. If Biden stepped aside, I might consider not voting.
