Why do we need a large number of witnesses from a Town?

In old days, Muslim Qadis from Morocco to Yemen and Central Asia and Afghanistan to Bangladesh had to announce "official" dates. They determined the 'reasonable' number of witnesses to establish the beginning of Ramadan and for Eidain dates. Please keep in mind that the number of witnesses was for each town or city, as the means of communications were not available to find out what was going on a few miles away.

1. Imam Abu Hanifa, Imam Malik and Imam Ahmad required a large number of witnesses (for a town, not a whole continent) when the sky was clear. (Bidayatul-Mujtahid v.1, Hidayah, Radd al-Muhtar, etc.)

2. Imam Shafi’ accepted two witness for Ramadan and Eidain

3. Hadrat Ali

4. Imam Abu Yusuf required 50+ in Baghdad (He was the Qadi).

5. Imam Abu Yusuf and Imam Muhammad required a group from each mosque in town. (Such a large number that could not be discredit)

6. Imam Khalf b. Ayyub asked for a minimum of 150, later raising the number to five hundred in Balkh. (Bahr al-Raiq)
    

Hadrat Umar (R) as the Khalifa did not accept the claim of a sighting by someone if the moon was not visible to others, including him, at the same spot.

Imam Shafi'i restricts Matl'a to the distance of travel for making "Qasr". Others extend it to 400 miles, the distance between Medina and Damascus (Syria). Ibn Abbas (R) did not accept Kuraib's sighting report in Syria 30 days ago as the moon was NOT SEEN in Medina on 29^th evening. Ikrama (a Tabi'i) did not accept sighting in "Astara", some 20 miles away from Medina as valid for Medina (Musannag Ibn Abi Shaibag.

Witnesses should be extremely sure to claim that they really saw a crescent moon and not a cloud, or a jet trail on the lower horizon.