The whole flow is so much better than card purchases, where you have to enter all the data (or see your password manager's autofill fail) and then you have to go to your credit card provider's app to acknowledge the transaction.

Cards are accepted by far more merchants,

The vast majority of Dutch online transactions are done because pretty much every Dutch online shop supports it. Also many international shops through Shopify and Stripe. Many Dutch online shops do not support credit card payments. So iDEAL is the far lower friction option here. And there is no American company in between (at least for most national payments). It's great to see this system, that served us two decades by now finally get rolled out across Europe. They tried it before in the early 2010s, but the non-Dutch banks were fighting turf wars.