I'm trying to understand why some things like the MenuBar and ContextMenu use swing underneath. They use the interop api instead of just drawing it directly with compose. wouldnt it be easier to use compose, or am i missing something?

I don't know if this is the official reason, but I think early on the reason was that it works, so don't reinvent the wheel until you need to

Menubar on Mac OS X is not part of the window, so we can’t draw it with compose.