Payouts that are processed right away are up to 4-6k seems quite acceptable to me.
It would also be illogical if very large amounts were automatically paid.
I can live with this policy myself, but I have not tried this site so I can only give my opinion based on the information from the op.
Yes, that is the only reason why they are caped..
You can test anytime by yourself, or hopefully someone will confirm in this topic later