I mean, they did bring Sonic 2 to PC but they just used the precursor to what is now Kega for it. Though there can be obvious advantages to actually translating the code over running an emulator, you don't have to worry as much about things like audio. For as much as there is to appreciate about S&K Collection and Sonic CD at the time, I find them hard to go back to specifically because of how awful the sound quality of SFX is. If you're going to write an emulator to emulate the way Genesis sound hardware works, may as well also build all the other parts too so that you can just run stuff out of the individual ROMs. Sure, more up-front investment but means you can sell more games.