I think because the GAAP metaphor is that revenues and expenses determine profits, which accumulate into equity, which is claimed by equity holders according to

I think because the GAAP metaphor is that revenues and expenses determine profits, which accumulate into equity, which is claimed by equity holders according to fully diluted shares. SBC was "supposed" to be accounted for by calculating dilution of the newly issued shares. The expense approach is basically a shortcut for analysts.