if twilio can not differentiate between inbound messages that are being forwarded and outbound messages that are created by the twilio customer then their service can't guarantee to be reliable because someone could basically create a DOS attack by sending spam to any twilio customer expecting that twilio will blame their customer and suspend the account.
It's not their job to differentiate they are just a carrier they scan for outgoing spam to protect their own core business and to not get blacklisted everywhere. Read the ToS they are pretty specific about it.
but then they are simply not suitable for the use case of forwarding inbound messages because the risk is to great that i'll get shut down just because i am receiving spam.
