Probably no big external dependencies or any assets. It looks like something full of handwritten code, down to the self-rendered UI-elements. Also it's written in C/C++ and assembler, so there is no unnecessary bloat shipped out-of-the-box.

Because they're good

And it's good. It also seems to have the most flexible plugin system of any DAW that has decent level of usage.

Or you know… build a proper app.

yeah, that's what i'm saying