Because it makes absolutely zero sense within the whole Biblical narrative framework -- the Tower of Babel was many generations before Abraham (and not located in Egypt!), the Pharoah of Moses was many generations after Abraham and many centuries before the Exile, and the book of Esther was over a century after the Exile.
There are plenty more such errors -- the Qur'an renames the first Israelite king Saul as "Talut" in order to rhyme with "Jalut" (the Arabic name of Goliath), and ascribes to "Talut" mainly the deeds of Gideon-Jerubbaal (a completely different person).
And the fact that Muhammad applies the phrases "Daughter of Imran" (i.e. Amram) and "Sister of Aaron" to Mary the mother of Jesus seems to indicate that he confused Mary with Miriam the sister of Moses (despite the fact that the two women lived over a thousand years apart)!
That's nice -- he still knew very little about the Bible or Jewish history, except what he heard orally by word of mouth from random Jews and Christians who happened to pbutt by. Muhammad never read a single word of any Jewish or Christian scriptures, which explains why he garbled so many Bible narratives so badly, and indiscriminately mixed parts of the Bible together with much later folkloristic legendary elaborations (midrash tales, etc.).
-- Some Qur'an quotes: 5:20 qaala muusaa 5:21 "yaa qawmi «dkhuluu «l-'arDa «l-muqaddasata «llatii kataba «llaahu lakum" 17:104 waqulnaa ... libanii 'israa'iila "«skunuu «l-'arDa" In English: Moses said, "My people, go into the Holy Land which God has buttigned to you!" And we said to the
