Because these types of trackpads need special drivers these days e.g. windows precision drivers.
Even basic things like palm rejection is done in software and for this one to switch between keyboard and trackpad in the fly you’ll need very good software that can predict just what you were intending to do.
Most "windows precision" touchpads are handled in Linux with just one module. Even Apple's Magic Trackpad can show up in system as a regular mouse (although with limited functionality).
Palm rejection is a thing that kinda makes sense to handle in software. For this thing, I'd expect firmware to be actually a bit beefer than usual.
Even basic things like palm rejection is done in software and for this one to switch between keyboard and trackpad in the fly you’ll need very good software that can predict just what you were intending to do.