It's funny to end up in interfaces/UIs of previous generations. Like today I wanted to stop part of an order I just made and ended up in some old legacy view to select which item order I wanted to revoke.
It would probably be little work to renew this page, at least adapt it visually to the current design. But they just don't care. That wouldn't create value I suppose.
While you may be right, I can tell you from experience that what seems simple can sometimes be embarrassingly complicated at Amazon. I previously worked there and my team once spent 2 months adding a new option in a dropdown box. This was on one of the seller-facing pages.
There are parts of Amazon that have a ton of legacy code and ownership between those systems can be a real mess.
It would probably be little work to renew this page, at least adapt it visually to the current design. But they just don't care. That wouldn't create value I suppose.