The key difference though is the nature of the 'gaffes' themselves. Trump's are embarrassing at worst, but the problem for Biden is that he ends up saying the quiet part out loud - stuff that is often patently racist and would give the media a collective aneurysm if it came from Trump
When has Trump ever said stuff like black people aren't as diverse as Hispanics? Or that poor kids are just as bright and talented as white kids? Or that Barack Obama was the first bright, clean and articulate African-American? Or if you don't vote for him, "you ain't black?"
Nine of this matters to the press though, because Orange Man Doubleplusungood