As mention upthread, AmEx is not an option through the digital wallet, even though AmEx said so via direct communication and eBay says so on the payment page. So...I don't know who came up with this plan.

I am not sure eBay or AmEx care enough. No question that eBay popularity has dropped off, but they still process over 70 billion in merchandise volume and 10 billion in their own fees revenue.

https://www.businessofapps.com/data/ebay-statistics/