Unweighted keyboards tend to have simple springs to return the keys to resting position, and more importantly, the cheapest instruments tend to only have note-ON;note-OFF characteristics due to being unable to sense any variation in how a note is played. These instruments playing all notes at the same volume is a natural consequence of inadequate sensors.
Returning to your sample values, MIDI 1 only directly supports 256 levels of volume, I think? This 8-bit level of variation is far lower than what any normal human sensory input can be expected to discern. MIDI 2, which was still very rare when last I paid heed, is a substantial improvement for potential expressivity. But even many years later, most consumer-grade instruments and playback devices only supported MIDI 1, sometimes with extensions such as GS or XG. The most expressive of the pro or semi-pro instruments that I've experienced have only seemed fully capable when using their internal proprietary enhancements; when outputting to a MIDI 1, the results were much less impressive.
As an aside, I've played only one piano whose keys felt as lightly weighted as my first semi-weighted keyboard and I found it a delight to use. Fully expressive, and less effort for the same effect as other pianos. I felt like I could play it for hours without tiring. By comparison, keys on all other pianos I've tried now feel quite heavy. I wish I could have afforded that one at the time. Sadly, memory of its make and model are long garbage collected.
