Personally, I like the idea of using bindings more than using GDscript* in Godot and my preferred language outside of Godot. From what I've seen, even if not perfect it's much less likely to cause confusion having 1 workflow (+some extra context in Godot) rather than 2 (not just syntax, but also technical stuff). Also it's nice to use code that doesn't actually depend much on whatever engine/framework you happen to be using it in (particularly an imported file with procedures).
Though some of my perspective may be that I haven't really used the language that I want to (mentioned in other comment) aside from a bit of tinkering with Raylib bindings (and a bit with Godot 3.X), so (aside from switching back-and-forth making less sense) I need Godot to learn the language just as much as I need the language to use Godot, all the things that motivate me (starting points for projects) are in various stages of viability particularly with how they relate to each other. Which admittedly is not the type of situation people wanting C# are in (...maybe some are with 4.X C# limitations).
Well, that and lacking writing/ideas for actual content. For instance I coded a basic adventure book reader (CYOA-type thing) but had no desire to actually write a story (so I didn't develop it further).
*= I would not totally be against using GDscript (particularly as the language I want actually isn't too different syntax-wise) particularly as I gain more experience, but I don't think it would serve much of a benefit unless it was for a specific calculated reason. As in not my first-step or common use of time. Same with other languages, for instance something like a networking system could be done in any supported language thanks to how Godot handles languages. And that reason for a different language could just be what someone contributing to a project prefers.