Because its not just Rosetta. Rosetta is just a translator for code. Apple would have to compile and test a PowerPC version of ALL the OS libraries. People think its just including some minor bit of code to make Rosetta work. Its not. Its Apple having to literally make two versions of its OS and test them. Most of that code will probably work just fine as its high level C, but some of it is assembly. And testing is where the real time sink is.