Why do Saturation and Luminance go all the way to 240, but Hue goes only to 239

The number 239 appears in the headline, and nowhere else.

I think we're meant to infer it from the sentence "Hue is endpoint-exclusive (because 360° = 0°) whereas Saturation and Luminance are endpoint-inclusive (because 1.0 is achievable)." They could have left in 240 if they wanted to; it would just duplicate 0.

This is shrinkflation! Windows is stealing 17% of the possible RGB colors from us.

I like that '239' is in the title question, but not in the article, yet the question is answered.