I think this also has to do with how "we" refuse to speak of left and right as actual sets of ideals as opposed to relative positions. As far as voters go they see themselves as centrist because they aren't far right fascists so they're to the "left" of them, but they don't agree with "the left" so they're to the "right" of them. Their actual beliefs though would make them conservatives and so right wingers...
As far as politicians, they just want to get elected and the Bidens of the world know they can't win as Republicans especially today.
People who call themselves centrist, are uneducated in regards to political terms. They don't know what they are talking about, but assume they do and they never go out of their way to educate themselves on these matters.