Why?
Looks like a good range if you want some quality.
And the resulting 'quality' appeals to you?
Only if there is a genuine demand, and they can operate that sensor as a 16-bit device (like the IQ3 100mp). Anyway, one can simply underexpose and push in postprocessing, which will create a similar photon starved capture as with a high ISO setting, but now with specular highlight recovery potential.
Cheers,
Bart
Actually, the reasons come down to marketing - Hass can treat 12k/25k as H1/H2 and make it so you have to enable them, but really, to have the same chip with different spec's is asking for communication problems. Yes, they're noisy, grainy, color being off, etc. We've known from the Pentax the ability was there, even video, just a business decision to limit it.
The reason for the higher ISOs as a setting rather than a mental calculation has to do with the meter - If you shoot it at -1 or -2 intending to pull up in post, the highlight warning and the image preview on the screen won't be accurate. By shooting at the higher ISO setting and at 0 your preview will be closer to what the final image will be, quality being ignored.
-Joe