I agree with you 100%. I just want something that stores files and works with SFTP and NFS out of the box. I get so annoyed every time I have to use S3 manually.
However, there is a post on this site that has become infamous in which a commenter questions the need for Dropbox when stuff like SFTP already exists.
SMB is absolutely terrible over latent connections.
I don't understand how SMB could work unless there was geographical replication to nodes closer to you, with some kind of load balancing to change the endpoint you're using to be closer to you.
I tried it a little less than 2 months ago across a suite of services, Azure, self hosted, AWS EC2 instances, and all of these same options again with WireGuard over the top (well, with Tailscale in this instance).
However, there is a post on this site that has become infamous in which a commenter questions the need for Dropbox when stuff like SFTP already exists.