They say here[0]:
We are currently paying near the 10,000€ mark per month and our revenue streams are at 1,500€.
The infrastructure and micro-services of soup became more and more complex over the years and the amount of data is huge, really huge. To serve nearly 6 million users is a resource-intensive duty.
This is also the reason why we dropped the idea of open-sourcing soup. It's too complex to maintain and to hand-over.
Hard to know where the $ are exactly going, but $11k/month will buy you a lot of server. Sounds like maybe just wasn't worth it given the revenue but I've got to believe it could be rearchitected so at least the hosting portion was profitable.
[0] https://kitchen.soup.io/post/696542642/Thanks-for-your-feedb...