Its not FOSS, and they rely on subscriptions. Call me a hardliner, but that's two non-negotiable things when it comes to nice-to-have software for me personally.

If they created an open source version I could self-host, I would happily adopt it. Frankly it looks beautiful and is only missing easy file integration. But they don't because it would cause them to lose a vast source of value they provide to their customers (providing proxies and servers for people to access their data remotely).

They rely on subscriptions for two very subscriptiony things - storing and syncing files, and hosting a website. Both have ongoing recurring costs, so a subscription is the only thing that makes sense. You don't actually need either of them and could easily use any other third party syncing/static host tool or service, and many people do with Git, Dropbox, etc.

The only part of their business model you can't go around is the fact that they're not FOSS, and for business use you need a business license. I personally find the terms quite acceptable (only apply if you work in a for profit place with more than two employees and more than X revenue), and the price is good value for money for me.