Sony HEIF: Why no Adobe RGB?

Last month I bought a Sony A6700. I still have mostly m4/3 gear and still mostly prefer it, but I was sort of bored and felt like trying something else.

Anyway, I have been playing around with HEIF photos. Sony, Canon, Nikon, Fuji, Panasonic, etc. these days produce 3 types of photo files: raw, 8-bit JPEG, and 10-bit HEIF.

With the A6700 the HEIF choices are: 4:2:2 or 4:2:0.

And you can select among 4 compression levels (same as for JPEG): Extra Fine, Fine, Standard, Light.

With Sony HEIF you can use sRGB or HLG (Hybrid Log Gamma) that uses BT.2020 color, but not Adobe RGB (choice is grayed out). With JPEG you can use sRGB or Adobe RGB.

I wonder why Sony HEIF does not allow Adobe RGB?

I have been playing around with HEIF 4:2:2, Fine, sRGB. Lightroom Classic supports it.