Sadly pretty normal for European companies. The penalties they face for signing up a bad customer are so much harsher they won't risk letting just anyone sign up without actual KYC not just checkbox KYC. This is the same reason Hetzner turns away 50% of its customers.
I used to work at Stripe and they subject to the same penalties as Ayden. There is a misconception that Stripe is an American only company, they have dual HQ model in Ireland and San Francisco. Since they are an Irish founded company and they have an EU entity “Stripe Technology Europe”. They can be kicked out of entire countries and regions if they didn’t have an extensive KYC systems and be fined just the same.
Since Stripe operates by working with a BIN (banks that sponsor them within each country) generally like all payment providers. While the decline rates for new customers are not public, they are very high, especially for industries that aren’t allowed like Adult Content, Weapons, and Gambling [1]. Also revocation of existing accounts can happen often if KYC systems flag anything, like Stripe Identity, Connect, and Radar.
Mollie (also Dutch) existed even before Adyen (and way before Stripe). They have no problem dealing with small customers, and have always offered a trivially easy to use API.