Because the tool doesn’t work well enough to justify their pricing
While I never ever use klarna because I don't like the idea of making payments on everything, the one time I did on accident click klarna pay instead of simply using my credit card figuring out how to undo it was great. I simply called their helpline, it went straight to a real person, and I explained to her I didn't need a 5 year payment plan on 30€ ski poles. She said she completely understood and said I could simply pay the full amount immediately and she would cancel the loan. That took like ten minutes tops to fix and it was certainly my fault for clicking the wrong thing. So their customer service is great in my experience.