Is there any way we can know that all these rules are from the Buddha and not made up after him, based on cultural and/or persons agendas?
People (e.g. those having left home, having left stinginess) who have mastered the fist step, who have gained the strainless eye of Dhamma, have neither doubts nor do they ponder much about it.
So why, if really like to know, don't simply follow them and why, if not follow them ponder about that much, being not you issue yet?
If seeking for doubters and waste a live by pondering around, there is a community working hard on being wiser as the elders for more then 2500 year. Simply join, there are plenty on topics on it. It's like science or watching news, everyday some new personal opinions.
If more tend to uproot doubt, to know for youself, avoiding association with doubt, foremost outwardly and also inwardly. Associate with admirable friends.
[Note: This is a gift of Dhamma, not meant for commercial purpose and other low wordily gains by means of trade and exchange]