This is because all written documents were destroyed by the changes of the empires through the history. The Abbasids destroyed everything prior to them, the mongols collected and burned each written piece, the crusaders in muslim Spain did the same.
When Ghazalis sect survived over Ibne Rushd all science, law and philosophy books written in Islam were destroyed by the muslim king that time. Thats why we cannot find much documents from the past.
Later kingdoms and the colonial forces ripped and destroyed a lot of islamic heritage.
The other important thing to know is that Ibne Hisham and Ibne Isaac were crypto jews. They planted fasle stories about the Hz. Mhmd in their writings.
After the mongols four new books were written and todays Islam is based mainly on those four books.
All hadees litterature were fabricated by non arabs that time.
By the way written Quran from the time of Hz. Mhmd can be found in the british museum.
Two letters written by Hz. Mhmd peace bee upon him are present today, those letters were written to Rome and persian empires.
Its a strong theory which suggest Petra being the birth place of Islam and Hz. Mhmd. Not Mekka which was constructed during the Abbasid time.
Kaaba was destroyed by a person named Zubair in Petra which was part of Syria that time, and rebuilt at a new place, which is now called the city of Mekka.
Elleven mosques before the time of Abbasi dynasty have their Qibla pointing towards the ancient city of Petra, and not Jerusalem.
Al aqsa mosque were build much later in the hostory.
Later kingdoms like the saudis and the rest of kingdoms in arabia did the same. They destoryed everythong prior to them. That because their countrymen would forget all prior to them and only obey their lordship.
Iran and Saudia arabia are two big evils who are splitting the muslims world for long enough time, in later history.
پاکستانیُ سیا ستدان ۔۔۔زادے کسی غلیظ ۔۔۔۔کے بچے ملک کو لوٹ کر اپنی ۔۔۔۔کے خصمُ عربوں کو بنا کر یہ ۔۔۔۔زادے ۔۔۔کے بچی وہاں اپنی پاکستان کی لوٹ مار وہاں چھپاتے رہے اور وہاں کے کے اقامے لے کر یہ ۔۔۔زادے منی لانڈرنگ کرتے رہے