Dutch resident here. Me and my two Dutch roomates order from amazon.de all the time, though I do agree bol and coolblue or similar are our first goto just because shipping is faster and cheaper.
With that said, they absolutely do accept iDeal and other Dutch forms of payment. I literally just paid for an Amazon order a few minutes ago with iDeal
iDeal is used in germany, but I dont think (not sure) it is common in the UK. Likely explains why if thats the case. I cant remember if my recent purchases off amazon UK offered iDeal as an option.
I think the biggest reason other than shipping cost that dutch people avoid amazon if they can is simply because its not in Dutch, and if you use the german one its not even in english. So it can be hard to find what you want.