Because Near East nations do not record defeats - the lack of ANY Egyptian records or texts or inscriptions to this end strongly confirms the Exodus account detailing the greatest defeat ever suffered by a Near East nation.
The lack of evidence for one thing does not evidence another. Just because they didn't keep records of their defeats (I am assuming you are correct) doesn't mean that the lack of records means they were defeated.
That is like saying "Bob usually doesn't take notes if he reads his science book twice or if the chapter is easy. Well, looks like Bob took notes, he must not have read it twice." It is nothing more than an unsupported assumption that favors your argument.
If ten thousand persons with Ph.D.'s say porn does not harm kids this means they are secret pedophiles and brazen liars.
-Willowtree