The company's root are of a gamedev (Over the Edge Entertainment) and recycled their in-house engine as a product. Godot Engine has similar roots (look up OKAM Studio)
Mostly because it is the only available option if one wants C# instead of C++ with great tooling, asset store and official backing from platform owners.
None of Rust libraries is even close of getting there, even the studios that apparently support Rust, are shipping on Unreal.