Interesting question, but it is quite complex.
Amazon is a retailer selling to end consumers so the banking opportunities (sure we can help finance those products you want to buy from us) are quite different compared to Facebook, for example.
Facebook does not yet sell physical products to end consumers. Google's main business like Facebook is in advertising, I am sure the additional personal information from banking services could be used to enhance their product offering to advertisers.
As for banks,which are still very powerful and influential, would they want their business disrupted by some large US or other nation's corporations?
This goes for most countries, but I can see the EU having reservations about any additional financial personal information being processed by Google, Facebook, Amazon and don't forget Tencent!