There are big stores that accept bitcoin. There are also big shopping centers in Japan and Korea where you can buy things with your bitcoins. I don't think it's just about regulation. It could be about the risk involved. There were a lot of scams and hacks and adding bitcoin payments could make the amazon payment system more vulnerable or at least this is how the management sees it.

If you want to buy stuff on Amazon you can buy a gift card with bitcoin and charge your amazon account with it. It's more work than buying stuff directly but not very hard to do.