Because centerstage requires iOS to run. It’s not something you run from e externally connected Mac.Like I said, I understand the engineering rationale. (BTW I think it's an A13?)
That being said... why doesn't Apple just run the Center Stage software on whatever Mac is plugged into the monitor? And if you're plugging a PC into the monitor, you wouldn't get Center Stage, another reason to buy a Mac, win-win for Apple...
Confusing question, because neither the iMac nor the MBP have "desktop speakers." I'm talking about independent, separate speakers that you put on a desk(top).
The ASD has down-firing speakers, meaning that output above ~300 Hz is crap. If the ASD is anything like the 5K iMac then I'm sure Apple has done a good job with the bass, meaning that it will sound rich and full and impressive if you just listen to some music casually for a minute or two, or compare it to laptop speakers, etc.
But pretty much any speakers you can buy that you can actually point at your ears are going to sound more crisp and clear.
Personally I have a pair of nice passive bookshelf speakers connected to a USB mini-amp. I'm sure most people would think it's overkill. But for under $200 there are some great options for near-field listening these days. If anybody asked me for a recommendation... search Amazon for "HiVi-Swans OS-10".
Sure you can easily run https://rslspeakers.com/pages/rogersound-labs-ia255-1-integrated-amplifier plus any unpowered speakers such as https://rslspeakers.com/products/cg3m-bookshelf-speaker
I personally use a kanto ORI pair with 8” sub. See https://www.kantoaudio.com/powered-speakers/ora/
The swan are no where as good for desktop comparably as the Ori which are usb-c with bi amped, and DSP based.