I remember when Dropbox was new and it was possibly the only solution I could find to seamlessly sync files on multiple computers (or at least the only one I knew about).

There was this "Dropbox" folder in your home folder, and anything put in there would show up in the home folder on your other computer or operating system or eventually even your phone. I also knew about Apple File Sharing and it was basically that but much more intuitive and worked on separate networks and on Windows (maybe Dropbox was inspired by AFS and the write-only "Drop Box"). Drop Box just worked, and to less tech-savvy younger me that was the only thing that mattered.

Now we have 300+ other programs which can do the same thing, and I use Git/Github for syncing and woof/AirDrop for individual files, so no Dropbox for me. And probably not for most technical users either.

But the average non tech-savvy user still needs a cross-platform service which "just works". And I'm sure their are alternatives which also "just work", but Dropbox is popular, and they don't care about the telemetry.