I saw, I just don't understand the rationale for picking Babel over OXC or something else as the interchange format -- other than "we were already doing it this way". After all, you know what they say about temporary solutions.
The current developers surely are more familiar with the Babel representation than OXC, so why switch?
This is just how software development for a large public project goes. If you want to land big changes in a finite amount of time, you take the path that breaks the least number of things along the way.
Once the whole ecosystem is rust-based, they can always trim out some of the redundant intermediate representations for performance gains.