@wdlindsy I think that’s one reason. Another is that “Incumbent president overwhelmingly wins primary” is a boring story (in terms of horse-race). It’s more interesting to pretend that there is a serious primary challenge to Biden.
Moreover, the political media is geared to covering process stories rather than stories about the merits of the underlying policies. These stories are way more interesting when you have an unstable authoritarian whacko in the White House.