Well it was a guess. That's why I qualified myself with "I may be full of it". There isn't enough information about their system to make a serious assessment.

Maybe they did. Maybe they decided it's possible but would take too long and they can't afford the loss meanwhile. Maybe they explored options but don't have the right knowledge.

But 10k€ monthly cost for serving 6 million users seems avoidably high unless it's something compute and data intensive like gaming.

It seems like a perfectly normal cost, even a sensible choice, for a cloud-based, invested-in startup with cash to burn that is optimising for speed to market and growth. But not for one that is cost optimised.

All that said, I wonder if their cost is actually mostly on people to run and develop the thing. Other comments have taken it as meaning the cost of infrastructure, and I ran with that. But soup.io's own note does not say it's all on servers.

If that's the case, obviously it's a different situation and there may be no reasonable way to reduce the costs below revenue.