Sony could absolutely make a PS3 emulator. Not that it would be easy per se, but they wrote the API and the made the chips, they have intimate knowledge of how it works.
They can also hire really good programmers to work on it. Emulators you see for free suffer from a few things that keep them from being as good as they could be:
1) The programmers don't know everything about the system. They don't have access to the design docs, the original code for the firmware, etc. They have to reverse engineer things.
2) They are doing it as a hobby. It isn't paying the bills. So there's only so much time and resources they can devote to development. Even if they really enjoy it, they gotta eat like the rest of us.
3) They are not always the best at the kind of programming they need to be. They are the people who think this is cool, not necessarily the people who know a lot about how to optimize processor architecture on a low level.
Well, none of these are a problem for a company making its own emulator. They have the code, they have the design docs, heck they probably have the people who designed the thing. So their developers can get all the information they need. Likewise the devs are being paid to work on it full time, and there can be a larger team, and support from other units and such. They can devote lots of time and resources to it as that is literally what they are paid to do. Finally, they can hire people who have the right kind of experience to do a project like this well. Even if those people aren't that interested in emulation, they are interested in a paycheck.
So they can do a much better emulator, should they wish.