For starters I've never heard of Adyen until just now. So, perhaps better marketing?

It's pretty popular in the Europe and is a Dutch company.

Its only "popular" because for a long time it was the only choice in Europe pretty much. In several countries it still is.

It also was total garbage developer friendliness wise ~5 years ago.

Well, Stripe still isn't available in like one quarter of the European countries.

I had the unfortunate opportunity to integrate with Adyen around 2016-2017 and it was super painful. The API didn't make much sense to me and the documentation was hard to navigate and understand. It all looked very rough and rushed to the market.

Granted it was "a long time ago" but I can still remember the pain.

Had a very similar experience around that same time. However, Adyen provided much nicer built in reporting features than Stripe at the time which made Finance happy.