All filesystems that I'm aware of don't sync to disk on every write by default, and you absolutely can lose data. You have to intentionally enable sync. And even then the disk can still lose the writes.

Most (all?) NoSQL solutions are also eventual-consistency by default which means they can lose data. That's how Mongo works. It syncs a journal every 30-100 ms, and it syncs full writes at a configurable delay. Mongo is terrible, but not because it behaves like a filesystem.

Note that this is not "bad", it's just different. Lots of people use these systems specifically because they need performance more than durability. There are other systems you can use if you need those guarantees.

I'd argue with mongo a lot of people use it because it has fantastic marketing.

https://nemil.com/2017/08/29/the-marketing-behind-mongodb/