Did you notice it's mostly written in/for
Haxe?
Taking a decent-sized body of code written for a high-level cross-platform language/environment like Haxe, and integrating it into an native-code application which consists mostly of C and some C++ requires a very substantial amount of effort, both in design/planning and in implementation.
Think of it this way: The simple LOGO app "REPEAT 4 [ FD 10 RT 90 ]" is a _tiny_ bit of code, and took a second or two to plan and implement. However, migrating the same app to C/C++ would require
vastly more planning to replicate, both in planning (figuring out 2D gfx libraries, dealing with platform IO & gfx concerns, etc.) and in implementation (simply because it would take many, many more lines of code to replicate in C/C++).
The problem moving from a high-level language and environment to a platform-specific low-level language is that first you need to figure out how to replicate all the environmental services and abstractions by the high-level code such that equivalents are available (where possible) for your low-level language coding. Then, not only do you have to implement low-level code to produce the same results, but also to replace any high-level environment services you weren't able to easily replicate (or for cases where the high-level service doesn't "mesh well" with your platform).
It's not that it's impossible, but it's a HECK of a lot more work than integrating the same app if it were written in C/C++ for Windows or similar -- that would actually make the job much easier, mostly because it's at the "same linguistic level", and dealing with the same environmental services/abstractions as LW itself (and they understand how to map those to Mac, etc.).