Because there's no Charles Bishop Weyland in the W-Y Report.
But there is;
Peter Weyland, Keiko Yutani, Mitchell Kane &
"The scientists, researchers, engineers who dared to dream the future and create the improbable;
Sir Peter Weyland, Jay Kasic, Dr. Sara de Ville and Michael Bishop."
As for the idea that Michael Bishop's a Weyland?
"Sir Peter Weyland's only legitimate child." -Meredith Vickers W-Y Report.
With no mention of children, crushed under the Juggernaut.
There's literally a book released by 20th Century Fox-
which chronicles the history of the corporation.
You don't get anymore definitive than that.