> Setting up shared folders cross-platform is non-trivial for the average person
It's nontrivial for me either. Until Windows got a native SSH client, it was the same problem every time: do I install like an FTP server somewhere and use Explorer, or set up a samba server on my linux box or how even do I copy more than a few megabytes... I don't understand how normal people can do this if even I have trouble, especially between two different OSes. Probably usb sticks are the answer, but then normal people don't have micro-to-female-A converters to connect flash drives to a smartphone, or know that you can even do such a thing.
And so that's why I maintain https://dro.pm and, e.g. when implementing encryption (which I didn't end up implementing because it was literally impossible given the ~2020 state of browser support), one of the main requirements is compatibility. If it's not going to work on any potato, I might as well not have it half the time, because on my own hardware I can usually just ssh. Unless you really want to transfer more than a few gigabytes of data, this works reliably (good old 90s <input type=file>, no JavaScript magic in that part) and the occasional wait is better than having to do sorcery with custom software on both ends, also because I usually don't own the non-linux endpoint.