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).