Because she is a DOCTOR silly.
Crikey! She's not even a Ph.D.
from: the National Review ---- https://www.nationalreview.com/2020/12/jill-bidens-doctorate-is-garbage-because-her-dissertation-is-garbage/
...."Consider “Dr.” Jill Biden, who doesn’t even hold a Ph.D. but rather a lesser Ed.D., something of a joke in the academic world. President-elect Joe Biden once explained that his wife sought the degree purely for status reasons: “She said, ‘I was so sick of the mail coming to Sen. and Mrs. Biden. I wanted to get mail addressed to Dr. and Sen. Biden.’ That’s the real reason she got her doctorate,” Joe Biden has said.
"Mrs. Biden wanted the credential for its own sake. As for its quality, well. She got it from the University of Delaware, whose ties to her husband, its most illustrious alumnus if you don’t count Joe Flacco, run so deep that it has a school of public policy named after him. That the University of Delaware would have rejected her 2006 dissertation as sloppy, poorly written, non-academic, and barely fit for a middle-school Social Studies classroom (all of which it is) when her husband had been representing its state in the U.S. Senate for more than three decades was about as likely as Tom Hagen telling Vito Corleone that his wife is a fat sow on payday."