EDIT: Before you ask, no-one has cracked TWL_FIRM (the thing that lets you play DS games) because developers know it's only going to be used for piracy.
That's assuming that every single developer hates copyright infringement. Piracy really doesn't hurt sales nearly as much as people would think (if at all - most cases of piracy apparently happen with things that the pirate wouldn't have ever bought) It hasn't happened yet because people haven't figured out how to make it happen.
It's because, unlike the 3DS - which is OS-built from the ground up to run installed CIAs in the same way it can run ROMs to the point of being able to run cartridge-only titles as a CIA, or download-only ones as a ROM; the DS(i) isn't. Software needs to be run the way it was meant to be run, as simply redirecting reads isn't nearly as simple as it is with things like the PS2 or Wii.