Who is financially responsible when an Amazon package worth of the good amount of $$$ is stolen from the front door? Would Amazon easily full refund the purchase?
You didn't specify a jurisdiction. According to Amazon.ca (Canada)'s conditions of use:
Risk of loss and title for items purchased from Amazon.ca pass to you upon our delivery to the carrier or, if such items must cross an international border, then risk of loss and title pass to you when they clear customs.
Unambiguously, then, Amazon has no responsibility in such an event. In the specific case you list, the package was stolen from the front door. It's unlikely any carrier would claim responsibility in such a case. Your credit card may offer insurance which covers theft such as this. This is often offered as part of extended warranty or theft/loss protection.
Just because Amazon has no responsibility, they may still reimburse you. This would be done out of kindness, not out of legal responsibility. I have had packages go missing; I have video evidence they were not delivered, but did not need to provide (or even claim) this, for Amazon to offer a free replacement.