I might prefer potatoes, but you might hate potatoes.
If we were looking at dishes in a restaurant, I might think one dish is a better value, because I like potatoes. You might think that that dish isn't worth it if you hate potatoes. It doesn't mean that the dish is better or worse, just that we have different preferences.
I don't use sync myself, so I can't speak on what specific aspects other people prefer over the FOSS apps. They might trust the developer more because they've interacted with them for a while, they might like how the UI works with their specific device, or they might even just like the logo. At the end of the day, it doesn't effect me, as I can just keep using jerboa.