Keys stored in the bootloader are public as asymmetric cryptography is used there. There is no security reason why bootloader should stay closed, but we were quite hesitant to open it because that's the last piece of mosaic that our competition is missing from making a perfect TREZOR clone.
Anyone who wants to clone your code can just upload (unsigned) firmware that dumps the bootloader. The STM32F2xx's level 2 code protection does not prevent flash from being read by code that is running within the microcontroller. No, this won't get you the source, but if you're going to be making a 1:1 copy, you don't need source.