It's not that people who don't understand white privilege can't put themselves in another person's shoes but rather they cannot understand why or how someone can feel inherently less valued from a society that values white features more.
It is easy to put yourself someone else's shoes in one instance but not their entire life. It's like you thinking as a white person "Wow that guy is racist, what an *** but at least he's just one guy" but then you talk to your non-white friend about it and they say "Yeah I'm used to it, this happens lik…  Read moree on a daily basis" and all of a sudden you're slapped in the face with reality. You didn't even realize that there were enough people out there who hate non-white people for it to happen every day and that is because of your white privilege.
There is also unconscious bias that plays a role in this too, and people are even less knowledgeable on the truth about unconscious bias. Unconscious stereotypes that we put people into based on what we assume about them.