Re: the point being...
Primarily, it's because, as others have mentioned, nostalgia. It's just not quite the same running an emulator of any of the old computers on a PC keyboard and trying to remember which keys are mapped to the "special" keys on the emulated device, or even when the correct keys exist on the modern keyboard, that they are in different places [*]. Oh, and 'it's a separate "plug'b'play" device, no setup, no messing about.
* iT can be weird playing a game on an emulator that relies on the cursor keys when they are all in the inverted T shape we get now and they were in all sorts of different combinations on the older kit. The old TRS-80 layout, IMO, was great for games. up/down on the left of the keyboard, left/right on the right of the keyboard, so two fingers of each hand, and then either or both thumbs for space bar/fire and joysticks were not yet that common back then! Think Space Invaders or Asteroids, buttons only :-)