HUR: "We also identified other recorded conversations during which Biden read classified info aloud

BIDEN: "I DID NOT SHARE CLASSIFIED INFORMATION. I did not, with my ghostwriter, I did not. I'll guarantee it."

HUR: "We also identified other recorded conversations during which Mr. Biden read classified information aloud to his ghostwriter."

Why was Trump charged even though he was President and why Biden has not, he was vice-president?