If somebody commits to it in the primary, then their mind is already made up. It sounds like you're putting the cart before the horse here. People are voting uncommitted because of how they feel about Biden; their feelings about Biden aren't changing because they vote uncommitted.

This is actually good for Biden, because he can check the pulse of the electorate going into the general election. Polling data, as we know by now, is notoriously unreliable. This is a way to get a message to Biden about what's important to his voter base. Without this information, people might not show up to vote, and he might have no idea why.